I had the same experiences that Gs5556 had. When actively A/B'g the difference is hard to discern. However, just listening and relaxing something not quite right. I used to own a 390S as well and sometimes after a power glitch, it would power up with the polarity inverted. I would notice it as something "not quite right".
Polarity Questions..
My Mark Levinson 390S has a feature that enables you to program and store polarity choices per track per disc... I haven't put it to the test yet and I was wondering if others have experimented with polarity changes...I suppose along the path from recording to mass distribution it would be very easy to have polarity reversed several times... and how would it affect the sound just curious