Brian Eno-' Jets s/b (73) my goof.
and how about some of that electronics, hmmmm.?
Tangerine Dream-Encore (76)
Tangerine Dream-Phaedra (74)
Ash Ra Tempel-Starring Rosie (73)
Ash Ra Tempel-Inventions For Electric Guitar (75)
Ash Ra Tempel-Communication(76)
Kraftwerk-Autobahn
A lot of Ash Ra Tempel albums (including the ones you mentioned above) were released in quad (they may even be single inventory SQ?) by the German label they were signed to, Cosmic Music. There are also a whole bunch of releases by The Cosmic Jokers, Popol Vuh, Klaus Schulze, and Tangerine Dream (Atem and Alpha Centauri) in quad on the same label.
There's also the Bacillus/Bellaphon label in Germany that released a bunch of prog in quad (some titles weirder than others) including Nektar, Omega, Dzyan, Nine Days Wonder, and some other ones that I'm forgetting at the moment.
I think the common denominator between most of this stuff was Dieter Dierks, who ran a studio outside of Cologne and seemed to mix everything he did in the early 70's in quad. I think a lot of these titles have been re-released on CD with the SQ encoding intact - I assume the quad master tapes must exist somewhere as the multichannel layer of one of the Nektar SACDs was sourced from the quad mix. It would be nice if some enterprising reissue label could work out a deal with the original rights holders to reissue this stuff because even though it's the nichest of niche products, it still deserves to be heard.
If we're speaking just in terms of personal taste (and not commercial viability) my personal nominations would be for Argent, I think their catalog is a bit of a mess sonically on CD, and a lot of the music is really dense organ/guitar stuff (especially the later albums like Nexus and Circus) that would really benefit from the surround soundfield. I also think Focus would be a lot of fun in surround, their two quad mixes (Moving Waves and Live At The Rainbow) are both really entertaining.
And last but not least, I don't know if it qualifies completely as prog rock, but I'd love to hear The Eleventh House (Introducing and especially Level One) and Mahavishnu Orchestra (especially the 2nd lineup albums Apocalypse and Visions Of The Emerald Beyond) in surround. Those latter Mahavishnu albums especially would be quite something as there are tons of musicians (and sometimes actual orchestras) playing and I think it would be an amazing experience to be in the middle of all of that. In a documentary a few years ago Sir George Martin said that Apocalypse was one of his favourite things that he ever worked on, and I couldn't agree more.