Plinius SA250 Mk.4 vs. Pass Labs X350

You should check it out, but I believe the only difference between the MkIII and the Mk IV is the upgrade to Siltech silver wire.

I have owned Plinius (SA-100 Mk III) and currently own Pass (Aleph 4). I have heard the X-350, but not the SA-250 Mk IV. I would say that Pass unquestionably makes the better amp on the basis of detail, soundstage, neutrality, high frequency and low frequency extension. This was clearly evident, but the Plinius had such marvelous synergy with the other pieces in my system, it makes this comparison a much tougher one than it should otherwise be. The Plinius has that iron-fisted bass (although it is not that deep) , great dynamics, and a marvelously clean midrange, upper midrange and high end. I don't see how anyone else other than you can weigh the pluses and minuses, ideally comparing these two amps in your system.