I got to listen to the X350 and X350.5 side by side at a friend's place before pulling the trigger on the X350.5. (He sold the X350 and kept the X350.5) I still have my Pass Aleph Os that I just love dearly. The original X series (non-.5 series) strayed away from what Pass was famous for and resembled more of a stereotypical SS amp, sterile and cold sounding. The .5 series brought back that midrange magic that the original Aleph amps were known for without any sacrifice in terms of dynamic and bass control of the non-.5 series. We both thought the difference warrant more than just a ".5" designation.
If your Sophia is not power hungry, go with the X250.5, otherwise spring a little bit more dough and go for the X350.5.
FrankC
If your Sophia is not power hungry, go with the X250.5, otherwise spring a little bit more dough and go for the X350.5.
FrankC