As Elberoth sugggests, the XA.5 series is very conservatively rated, I can tell you that having owned the XA30.5 I would discuss it with Pass Labs, if they tell you it should be no problem, you can trust them.
Pass Labs A/B amps vs Class A amp and Actual Power
Dumb question; how can you compare the actual power or ability of an amp to drive a tough load (such as a Magnepan) when looking at a Pass Labs A/B design such as the X250.5 or X350.5 vs one of the full class A amps like the XA60.5 and XA100.5? For example, which amps would (from a standpoint of just pure power/grunt) drive 3.6's better, an X350.5 or a XA60.5?