The Quad debacle made good at least on one account : it forced the LP industry to heighten its technical standards so that LPs could contain enough coded phase-shifts to feed the Quad decoders and receivers.
The result was that regular 2-channel LPs bloomed with even more magnificence, a depth which some say we did lose with subsequent digitalia...
An evolution of the earlier SQD-2000 (1970), the SQD-2020 also had an SQD-2010 sibling and was, according to Sony's politics, strictly SQ oriented : SQ reel-to-reel, SQ LPs, SQ Radio broadcasts (oops, sorry : that one never made it either).
Sure, but it could handle QS coded sound. Or any other source as it were : spread a 2-channel source onto four channels or decode the QS coded sources by way of its R-Matrix mode or even be used in mono.
Mono, MONO ? Monophony over 2 speakers ? Spread over 4 ?
But it ain't mono anymore !
Go figure :-)