Quadraphonic FM stations, like quad itself, never really did catch on, did they?
[size=8pt]That's speaking of using discrete quad systems, like Dorren. But neither did matrix quad systems using more modern technologies like Dolby Surround, for some reason. (Excuse me, I guess they call it "Pro Logic" now.) Yes, my KQAC, KKCW and pretty much everything else recorded in stereo certainly are playable in "pseudo-quad" on a stereo receiver with a Dolby quad system, but I'd certainly call them proper "quad" stations like that due to the general lack of music that's actually mixed for it. Too bad.....post-1970s, in the CD era, that system did seem to have potential!
Oh, by the way, the original audio CD standard (the "Red Book") did at least partially specify a discrete four-channel process. Too bad that never amounted to anything, either!