I used to enjoy the synthesizer mode on my Audionics Space and Image Composer. Then it started malfunctioning. So, I started playing the stereo records in the SQ mode. I got to where I liked the SQ mode better than the stereo enhance mode. The stereo enhance mode had started working again later. So when I get my Involve decoder, I will try the stereo records in SQ and QS mode and see which I like better. I could see that it might even depend on the material being presented to the decoder. We will see how it does.
When I was using my Fosgate Tate 101A daily I don't think (or can't remember) ever checking out stereo in the SQ mode. My prior SQ decoder was a Kenwood 9940 receiver that had Full Logic with Wave Matching SQ. I do clearly remember trying to play stereo through SQ on that. I had to turn the F/B balance almost all the way to the back, and then turn the main volume up to compensate, just to get some kind of surround out of it. Later I learned that's because the way stereo recording/mixes are made simply do not approximate the SQ encoding at all.
Sansui products were not very popular where I live back in quad's golden years. So I actually had to build a QS/SQ decoder from a kit. This is the Photolume decoder Ken & I have talked about. Playing stereo through QS Synth and even just the QS mode was a jaw dropping revelation to me.
Most looking forward to your impressions of the SM v2 when you get it!