Agreed RE the QS version of Pretzel Logic - It truly is awful. I was curious though whether there would be a difference in upmixing from a SQ or QS encoded source vs a 'standard' stereo source. To this end, I grabbed PBTHAL's vinyl rip of the QS matrix and ran it and a high res stereo source (SACD) through DTS Neural to see what the results would be like. It is like chalk and cheese... The QS version achieves virtually no separation (i.e. double stereo as you noted above), whereas the SACD source gives quite a good discreet upmix. I then thought it would be interesting to see what happens with some other source material - so I gave various versions of 'Money' from DSOTM a go through DTS Neural. For this I have available PBTHAL's rip of the SQ Vinyl, plus the 1973 and 2011 stereo versions from the Immersion box set and the original 4.0 and 5.1 mixes (also from Immersion). The results were really interesting - as the 40 second clips here show
Pink Floyd - Money Source Comparison (starting from when the bass comes in).
The SQ mix through DTS Neural still has quite a bit of vocals in the rear starting at about 28 seconds, whilst the 1973 and 2011 have virtually none (1973 is slightly less than 2011). The kick drum is pretty much absent from the SQ upmix, and is stronger in the 2011 version than 1973. To see how all three compared to the discrete surround mixes (1973 4.0 and 2003 5.1) I have also included extracted rears from both. Of these, the 4.0 mix is
very discreet, while the 5.1 is very busy compared to all the others. Using the ABX plugin for Foobar, you can switch between all five versions to hear the differences
What would also be good to compare would be a decode of the SQ Rip against the discreet 4.0 Immersion version, but I don't have the necessary scripts to do this.