The engineers tasked with encoding four separate signal paths (quad) to a single V-groove pressed into a flat plastic disc had to have known that there was no way it would ever deliver discrete high fidelity quad, even that fiddly stroke of genius called CD-4 had its Achilles heel with its own practical difficulties.
It was the greed of record company accountants and lawyers (who were certainly warned it was a deeply flawed pursuit), that kept them hell bent on beating out their competitors at selling the public more quad as cheaply as possible, all because the alternative which at that time was all magnetic tape, primarily Q-8 and 1/4” reels required double the amount of recording material and therefore at higher cost.
A vinyl disc that has true quad content magically encoded to it’s one groove is essentially the same cost as mono and stereo to produce and get out into inventory.
That’s what drove whole push for all 4-ch matrix schemes for vinyl discs.
I will concede this much, when I listen to a QS disc thru the QSD-1 it is pretty cool, so I can say yes, they did a commendable job of it, the SQ is good too, my CD-4 works well also, but then, none of it is as purely 4-ch discrete, highly dynamic and “audiophile” grade as any of my 4-ch open reel machines, especially the Ampex ATR 1/2” 4-trk running mastering tape at 15 ips!
Even my tascam 234 quad cassette at its native 3.75” IPS outperforms my matrixed quad vinyl titles.
The big fly in this ointment is always the near impossibility of finding or accessing high quality properly mastered 4-ch versions of music that is so much easier to find on vinyl. We do have the boutique audiophile 1/4” stereo tape sellers offering a few select titles, but they are $350~$500 each! But of course, No quads ....yet.