I wasn't speaking of the DVD-A, which was a new 5.1 mix done specifically for that release in 2001, I was talking about the 1974 Warner Bros. quad mix. Unlike the majority of the Warner Bros. quad releases which usually carried the 'Re-mixed for QuadraDisc by' credit on the back cover, Machine Head has no such credit leaving the identity of the person responsible a mystery. I would assume it was someone like Lee Herschberg or Donn Landee or one of the other senior WB engineers, but there's no way to verify conclusively without interviewing some of those people.
Having said that, the 5.1 remix of Machine Head is also really good and the inclusion of the B-Side 'When A Blind Man Cries' makes it even more worth owning. The 2003 EMI SACD (which contains the EMI European quad mix) has 2 or 3 of the 5.1 remixes (including When A Blind Man Cries) tacked on at the end as bonus tracks.
Regarding your other point that AF should concentrate on unreleased quad mixes for future releases, I couldn't agree with you more in principle but they also occasionally have to go for the 'low hanging fruit' sales-wise and do some of these big name titles that have been reissued to death previously because they sell a lot of copies. Every big name title they do (even if they aren't necessarily as exciting to us) puts more money in their coffers and ensures that their reissue series continues. I think between Brian and Jon and all the people who've emailed Marshall/AF directly with their want-lists they have a very good idea of what people want - I doubt Marshall is sitting at the controls of his spaceship going 'well, I've had hundreds of requests for Santana and Edgar Winter and BOC and Aerosmith, but I'm going give 'em Mannheim Steamroller just to mess with their minds!'
If AF or other multichannel reissue labels haven't been able to get their hands on some of these bigger, more desirable artists it's not because they don't want to - you have to assume there's some kind of impediment to it happening, either legal, licensing, or just the major labels wanting to put it out themselves. Look at the Chicago Quadio box - Warners could have licensed those albums one at a time to AF or AP or MoFi but they chose to put them out as a box set themselves. If you look at it from their viewpoint, licensing makes sense for albums where selling a couple thousand is literally not worth their time. But for something bigger, why would you license an album to a smaller company that's going to sell 5,000 copies and split the profits with you when you can sell it on your own, sell way more than that, and pocket 100% of the profits? Personally I think that's why we haven't seen licensed reissues of Sony titles like Aerosmith, or the majority of the big WB artists (Doobies, Joni) and pretty much nothing from the UMG owned labels.
One thing about the majors though is that they love a proven formula, so if the Chicago Quadio box sells well don't be surprised to see WMG or the other labels doing similar sets for other artists.