I think like lots of people here, I'd read a few times that Vanguard was the first label to release anything in quad, and that they did so in 1969, well before any of the major labels, and I just kind of took it as true. I'm not sure what got me thinking about it, I got a bee in my bonnet recently and wanted to know more about the 5 W's (Who, What, Where, When and Why) of Vanguard's groundbreaking foray into 4 channel music, so I did some digging through some trade publications and found some interesting stuff.
The first was this news article from the July 5th, 1969 issue of Billboard announcing Vanguard's initial batch of releases. I think the remarkable thing for me here is to think of it in the larger context of what was going on at the time - we (or at least I) think of quad as a very "1970s" thing, but here's this announcement some 3 weeks before the Apollo 11 mission to the moon, and more than a month and a half before Woodstock, which seems like the zenith of 1960s culture.
It's also interesting to note how far ahead Vanguard was of almost every other label in releasing quad product - nearly a year ahead of Liberty/UA (July 1970), 18 months ahead of RCA (November/December 1970),and even further ahead of biggies like Ovation (1971), Columbia/Epic (1972), Warner/Elektra/Atlantic (September 1973), Stax (1973), Fantasy/Prestige/Milestone (1975) and Arista (1976). I also think the article (transcribed below in full so it's easier to read) does a good job of articulating the arguments for both ambient and discrete surround mixes, with examples - something that a lot of writing over the last 50 years has failed to do.
The next is a full-page advertisement from the November, 1969 issue High Fidelity magazine, chock full-o-quotes from a number of (presumably prominent) men of hi-fi extolling the virtues of the new format, and listing the first 8 releases (4 classical, 3 pop and a sampler). Interesting to note that there isn't one use of any variation on the word "quadraphonic" - no quad, quadrasonic or quadriphonic. I believe in the earliest days of quad there was some worry that someone might own the trademark on the word 'quadraphonic' so this may be why the announcement is worded as it is. Also interesting to note that the ad suggests that quad 'cassettes' are coming, a development which never materialized.
And finally, another full-page advertisement, this time from the March 28th, 1970 issue of Billboard featuring a sort of whimsical cartoon, and a list of most of Vanguard's quad reels. Interestingly, I don't think any of these were released on quad LP in the US (some were in Japan via Vanguard's licensing deal with King Records) or on Q8 - even the Country Joe and the Fish single-LP Greatest Hits was replaced by the expanded double-LP Life and Times: From Haight Ashbury to Woodstock compilation when Vanguard finally started releasing QS-encoded LPs in 1972.
(Also note they're using the word 'Quadrasonic' in this advertisement.)
I think there's probably more meat to be put on this bone, research-wise, but I thought this was interesting enough to share as it is - I was kind of struck by the fact that the initial announcement was right around the time of the first moon landing, because for surround sound music, the Vanguard issue of quad tapes was similarly momentous in ushering in a new era of recorded sound.
The first was this news article from the July 5th, 1969 issue of Billboard announcing Vanguard's initial batch of releases. I think the remarkable thing for me here is to think of it in the larger context of what was going on at the time - we (or at least I) think of quad as a very "1970s" thing, but here's this announcement some 3 weeks before the Apollo 11 mission to the moon, and more than a month and a half before Woodstock, which seems like the zenith of 1960s culture.
It's also interesting to note how far ahead Vanguard was of almost every other label in releasing quad product - nearly a year ahead of Liberty/UA (July 1970), 18 months ahead of RCA (November/December 1970),and even further ahead of biggies like Ovation (1971), Columbia/Epic (1972), Warner/Elektra/Atlantic (September 1973), Stax (1973), Fantasy/Prestige/Milestone (1975) and Arista (1976). I also think the article (transcribed below in full so it's easier to read) does a good job of articulating the arguments for both ambient and discrete surround mixes, with examples - something that a lot of writing over the last 50 years has failed to do.

Vanguard's 4-Track System
By Fred Kirby
NEW YORK - Vanguard Records is preparing its first "Surround Stereo" release: "a new simultaneous track stereo system, capable of reproducing music and the acoustical properties of the auditorium in which it was recorded."
This system utilizes four speakers: two in front of the listener to the left and right as in normal stero, and two at the left and right to the rear of the listening environment.
Seymour Solomon, Vanguard president, explained that his company's first release under the new system was scheduled for mid-September in a tape CARtridge or cassette configuration. He said he was conferring with other record manufacturers and equipment manufacturers on the reproduction system that will be used. Solomon said there also was a possibility of the three-dimensional recordings being available on reel-to-reel tape.
Among the major advantages of "Surround Stereo" is the reproduction of the actual acoustical properties of the auditorium recorded in and of surrounding the listener with the sound as though he were seated in a concert hall.
Under "Surround Stereo," the front two channels are recorded as in conventional stereo. At the same time, two additional channels are recorded through strategically placed microphones directed toward the rear and sides of the auditorium.
In addition to catching the reverberations of individual halls the system can be used in large works, such as the Berlioz "Requiem," which will be on the initial release with Maurice Abravanel and the Utah Symphony recorded in Mormon Tabernacle. This work utilizes four brass choirs located in different parts of the hall. Each choir is offered a different track.
"Surround Stereo" also has impressive effects for pop music with three of the initial tapes in this area: "David's Album" by Joan Baez, "Illuminations" by Buffy Sainte-Marie, and "The Amazing Electronic Sound of Jean Jacques Perrey." Also slated by Abravanel and the Utah are Mahler's "Symphony No. 3" and "Symphony No. 9." Vanguard also will continue to issue product on stereo and cartridges.
Solomon explained that Vanguard was in a better position to introduce this new sound system than companies with large investments in pressing plants. He doubted that "Surround Stereo" economically could be applied to disks.
Vanguard introduced the new technique to the press at the firm's headquarters here on June 25. Assisting Solomon with the presentation were Jack Lothrop, engineer, and Ed Friedner, manager of Vanguard's engineering department.
A basic theory behind the use of the four tracks is that from 20-60 per cent of sound heard in a concert hall is reflected rather than direct. By reproducing this reflected sound, it might even be possible to identify the hall a recording was made in through the differences in reverberation.
The next is a full-page advertisement from the November, 1969 issue High Fidelity magazine, chock full-o-quotes from a number of (presumably prominent) men of hi-fi extolling the virtues of the new format, and listing the first 8 releases (4 classical, 3 pop and a sampler). Interesting to note that there isn't one use of any variation on the word "quadraphonic" - no quad, quadrasonic or quadriphonic. I believe in the earliest days of quad there was some worry that someone might own the trademark on the word 'quadraphonic' so this may be why the announcement is worded as it is. Also interesting to note that the ad suggests that quad 'cassettes' are coming, a development which never materialized.

And finally, another full-page advertisement, this time from the March 28th, 1970 issue of Billboard featuring a sort of whimsical cartoon, and a list of most of Vanguard's quad reels. Interestingly, I don't think any of these were released on quad LP in the US (some were in Japan via Vanguard's licensing deal with King Records) or on Q8 - even the Country Joe and the Fish single-LP Greatest Hits was replaced by the expanded double-LP Life and Times: From Haight Ashbury to Woodstock compilation when Vanguard finally started releasing QS-encoded LPs in 1972.
(Also note they're using the word 'Quadrasonic' in this advertisement.)

*The revolutionary new Quadrasonic system of stereo, a simultaneous four channel technique capable of reproducing music and the acoustical properties of an auditorium in which it is recorded more faithfully than heretofore possible.
Surround stereo tapes now available include:
VSS-1 Surround Stereo Sampler
VSS-2/3 Berlioz Requiem
VSS-4/5 Mahler Symphony No.3
VSS-6/7 Mahler Symphony No.9
VSS-8 David's Album - Joan Baez
VSS-9 Illuminations - Buffy Sainte-Marie
VSS-10 The Amazing Electronic Sound of Jean-Jacques Perry
VSS-11 Handel's Jephtha (Highlights)
VSS-14 Greatest Hits - Country Joe and The Fish
(VSS-12/13 is Joan Baez's Blessed Are...)
I think there's probably more meat to be put on this bone, research-wise, but I thought this was interesting enough to share as it is - I was kind of struck by the fact that the initial announcement was right around the time of the first moon landing, because for surround sound music, the Vanguard issue of quad tapes was similarly momentous in ushering in a new era of recorded sound.