The S&IC does a fantastic job with stereo using the "Stereo Enhance" mode. The only time that I recall ever heard any pumping effects was with an SQ recording "Super Session" (SQ mode), and that was while using the unit with the older National Decoder chips. Backing off the separation control a bit eliminated the anormalities. My original unit has the Exar chips and never pumps, anormalities only show up in the rear channels while listening to them in isolation, almost never noticeable under normal listening conditions.I had an Audionics S&IC; playing stereo records through it in the SQ mode sounded OK, but with lots of "pumping". That's one major advantage of the Involve Surround Master; no pumping, and more separation.
QS surround has one minor advantage regarding stereo enhancement in that the soundfield is evenly pulled apart around the room; intermediate panned sounds will emanate from the left and right front speakers. SQ enhancement is more of an inverted V shape rather than an inverted U (like QS) but subjectively both the Composer and the QSD-1 produce a very similar enhancement effect. The Composer just sounds better, no noticeable degradation in sound quality, you can't say that about any other decoder.
The Surround Master does not have a "Surround" mode, straight QS enhancement of stereo sounds more like double stereo, just that the vocals are moved to the front not a lot different than Dyna Quad.
The Surround Master might have more separation than the Sansui units but not more than the S&IC does on SQ!