I have had an awful lot of high end Pioneer gear pass over my bench. I have not had any Sansui gear pass over the bench, so I cannot speak on a comparison basis. If you want to know what I have found to be the sweetest sounding "fully restored" vintage amp (not receiver), that has the Pioneer brand, it is, hands down, the SA-9100 (and its tuner, TX-9100). It is not the biggest, but it is the sweetest sounding amp I've restored, and I've done many of them. Compare that amp to a Sansui of like power, and I think the Pioneer will hold its own very, very well.
As for bias, I am a high end Pioneer restorer. In my main rig are 2 SPEC-4s (driven by a SPEC-1, all fully restored, including recap), which come very close, but the SA-9100 wins in sweetness and sonic ahhhh factor. None of Pioneer's receivers come even close to the SA/TX-9100 combo. That is all my opinion. Let your own ears decide.
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Enjoy,
Rich P