Oh yeah, I loved that 3340S. But by 1981 quadraphonic was already dead, so it never occurred to me to try making a discrete 4-track mix. My final medium was cassette, but I'd mix the 4-track to a second 2-track machine first. In those days I didn't really appreciate how much of the mixing work was being done for me by the cassette tape! Now I understand people's love for tape sims in the digital world (even though I don't use them myself).
Sycraft, thanks for the Foobar tip. I am a longtime fan of Foobar, but was unaware of the dvd-a add-on.
And thanks, John, for the quad CD link. My initial research had shown that although the original Red Book draft included support for 4 discrete interleaved channels, it was later dropped from the formal spec. Consequently, no CD players were ever built that could play back 4-channel data. But your link suggests that quad content does exist on CD. However, I am still unclear as to how one goes about playing them. It lists three different encoding methods but does not explain them.
I think for now I will just do a quad mix for my own amusement, and anybody who wants to hear it will have to stop by and listen on my newly-acquired headphones.