Gandme and Guidocorona, when I was communicating with Peter at Pass Labs at great length regarding if the XA amps, which did replace my 350.5, could power my MG-20r's in by-amped mode, one item that was clearly covered was that the overall sonic signature of the monoblock XA series amps does not qualitatively change, only the power/watts ratings.
This was very important, in that I noticed that the 350.5 at my loudest listening levels almost never left their Class A rating, which is around 50 to 60 watts. Therefore, it was decided that the XA-100's could drive my rig without distortion or compression. Otherwise, it would be on to the XA-160's at a cost of another $5000.00. Well, I'm no cheap skate and would have bite the financial bullet if I had to, in order to get the extra power if I needed it.
Well, I did not need the extra 60 watts of single ended Class A watts, to have the magic of the XA series in my listening room. But the major point regarding the three top XA models, 100's, 160's, and 200's is that their overall sonic signature is the same throughtout these monoblocks, the difference is their ultimate power ratings.