PassX-250 vs PassX-350

I spoke to Peter at Pass and he helped me with some of the differences between the amps. The x150 and x250 have similar circuit designs with only some localized feedback around the output stage. The X350 and larger amps have the zero negative feedback characteristic which adds to their lushness and overall neutrality.

Muralman1,
I thought that was what I said. Rather, what Peter said.
For $4000 used I'd also opt for the X350

Bhouser, Muralman1, I may have lost some of the details in paraphrasing what I was told so I thought I'd post the response verbatim. Sorry for any mix-up.
"In circuit design the X150 and X250 are very
similar. They both use some localized feedback around the output stage which bumps up their damping factor dramatically compared to the larger amps (X350, X600 and X1000). This higher damping factor contributes to exceptional bottom end, although the zero negative feedback characteristic of the larger amps adds to their lushness and overall neutrality. There are tradeoffs, always. However, all the X series amps are extremely dynamic, with very listenable top ends that are not forward or bright, and are very quick and responsive to musical transients."