Hate to disagree for once Sonic and yes I am extremely biased but on every listening test against the Tate I have done I can straight away hear the Tate in terms of sonic artifacts and gurgles on numbers I think its about the same maybe Tate has the edge but its not an audible thing
Wow you pack a lot into one sentence!
I know I'm on thin ice since I can't compare the Tate directly to the SM (the former is quite inoperative) I can easily recall my impressions & judgment of the Fosgate Tate to Sansui Vario-Matrix. One aspect little talked about is that the Vario-Matrix enhances the direction of a dominant sound while diffusing lower level sounds. If a lead guitar starts in left back & quite loud drums start in center front then the guitar direction becomes diffuse. That is what happens when separation enhancement is part if the actual decoding. However the brain will largely think the guitar is in left back because that is where it was heard first. I think this push/pull sharpen/diffusing action works in a subtle way, almost sub-conscious , but it's still there. The Tate system works after decoding so it generally just stays sharp & separation is enhanced with out any diffusion.
It could be argued that the vario-Matrix is more pleasing since the ear/brain combo likes contrasts in sensing direction. That's why the Sansui Vario-Matrix soundfield always sounds more full & round, if you will, than Tate enhancement, which always sounded a little dryer & thin to me, but also more precise.
The Sansui units all seemed a little bit warm sounding too me and the Tate sounded just the tiniest bit bright. I'd say the SM tonal wise is the most neutral matrix type decoder I have ever heard with any format intended to be used by it.
I also remember the Fosgate Tate 101A having better front to back separation than the Surround Master. There is bit of bleed through playing center front in SQ mode in the rear chs & I remember the Fosgate being silent.
Elsewhere you have given extensive data on the SM decoder using the Involve encoder to generate test signals but I don't think you've posted in the SQ mode which would be very interesting. Are you essentially using the same approach Sansui did for SQ? Seems I remember Sansui saying 12dB center front to back separation for SQ.
Of course your biased that's what test monkeys are for! Even that is not fool proof. I remeber plenty of articles during the testing of the Tate enhancement where listening panels said the decoded SQ sounded better than discrete. Hmmm.... My own experiment with QS encoding of Suzanne Cianni discrete tracks & played through the SM v2 I could not tell any difference between them. And really that is something.
Lastly the Fosgate unit had that groovy stereo synth switch that opened up the soundstage to a 270 deg or as some people have called it, a horse shoe. Even tho with numbers it can be said a panned signal left to right do the same thing on Sansui Synthesizer or the SQ Tate maethod, audibly they are quite different. Besides what is desired of the Sansui effect it also lowers the front ch atiny bit, raises the rear signals a bit & generally enhances the ambient reverby sounds. The Fosgate tate unit simply gives the wrap around effect & therefore, once again, it sounds a little bit dryer but more precise. At any rate I still prefer the over all "feel" to the Sansui method of enhancing stereo input.