I appear to have acquired a burned DVD-Audio of a quad mix of Meddle along with a similar DVD Audio of Animals.
For Meddle, the disk indicates that the version came from Q8. It sounds superb and does appear to have discrete channels, though I will not claim to be an expert as I have never listened to a matrix quad LP. The pictures show various Japanese vinyl pressings. The pics are very poor scans, but one of them shows a cover of the album with an obi sporting a large 4 at the top with two half-circles surrounding the numeral. The obi also appears to say something about Japanese TV, but the rest of the writing is too poor for me to make a guess about what it is all trying to say. All of the images show scans from various Japanese pressings of Meddle which differ from my own Japanese pressing.
A lot of products get released in Japan that never make it over to the western world. It wouldn't surprise me if quadraphonic vinyl had been released there and nowhere else. As for the Q8 claim, however, I'm not sure how popular 8-track tape was in Japan. It is my understanding that it was primarily a format used in America. There are, however, enthusiasts who have been looking for the existence of particular products for years only to be surprised that some things that had not appeared to exist actually do exist. A reel-to-reel copy of Meddle appeared in eBay last year much to the surprise of Pink Floyd enthusiasts.
The Animals disks contains both Q8 and SQ versions of Animals along with versions of Pigs on the Wing that were exclusive to the respective US and British Q8 versions. That there were various versions of Animals has been a frustration to collectors. Apparently, the reel-to-reel version had different mixes from the album as well, though I'm not sure if they were also different from the Q8 version. The pictures show various 8-tracks including a Q8 version. There is also a picture of the Japanese SQ LP with the number 4 flanked by half-circles just as on the Meddle pictures.
Something to keep in mind regarding determining the existence of particular recordings in a particular format is the initial method of distribution. While typical users went down to their local record shops for new stereo records and 8-tracks, audiophiles with special systems such as quadraphonic and reel to reel might more easily have purchased their media from the same store where they bought the audio equipment. Accordingly, these media enjoyed relatively small print runs and are hoarded by collectors. I must say that if I had a reel-to-reel tape of Pink Floyd, I'm not sure that I would have any interest in selling it. I think I would rather enjoy the pleasures of listening to it myself despite the high price tag such an item could fetch on eBay. Columbia House offered Pink Floyd on R2R tape into the early '80's, but those who have them aren't in a big hurry to let people know they have them or to give them up.