It was 1991 before I heard (most of) my CD-4 discs in quad, IMHO, the CD-4 quad to stereo folddown provided a good stereo effect, both thru speakers and headphones.
DV could even use DynaQuad encoding of the discrete quad mix for the stereo CD layer on their MCH SACDs, just add LB+RB and place this in phase is L and out of phase in R, could be decoded by SQ, QS, EV Stereo-4, speaker matrix since all of these decoders would route this content to CB.
I emailed DV some time ago about this, maybe I used the wrong email for suggestions or maybe I didn't explain myself very well, I'll try again soon.
Kirk Bayne