(disclaimer: I sell pass gear)
I would definitely go with the X350. If power is any question you want to get that amp. It jumps from the 'will power most speakers' X250 to the 'Will power ANYTHING' X350.
I have matched the 350 up with a Bat preamp (vk-5i) and found it was quite a nice combination. Since the Pass gear is so transparent it lets the character of the feeding source come out more.
(disclaimer: I sell Pass Labs gear)