Pass Labs X 350.8 or 350.8?

I've a small listening area (about 220 square foot), and I'm using below equipments:

Esoteric K-03X CDP
Lumin S-1 Network player
ARC Ref 6 Pre-amp
Electrocompaniet AW-180 Mono-block amp
Wilson Audio Sophia 3 speaker ( In the future, maybe I will upgrade my speaker to Shasha 1/2)

I want to buy a new amp to replace my old EC AW-180 Mono amp, my choice is between Pass X-250.8 and X-350.8.    Should I get X-250.8 because of my small listening area?  Or I better to buy X-350.8 for long term? THX.
I would go with the 350.8 over the 350.8.  Why do you want to replace the Electrocompaniet?
My understanding is the the X250.8 is a little sweeter sounding, but the X350.8 will have more power to drive difficult speakers. You may want to look at the X260.8 monos as well. Higher Class A (34wpc vs 17wpc before hitting Class AB) output to start with and might be more to your liking.
Hi theothergreg

My Electrocompaniet amp is already 6 years old, I want to get some new sound , just like I replace my  Electrocompaniet EC-4.8 per-amp with ARC Ref 6.,  and the result is amazing.

Now you have a different user name? 

What kind of "new sound" are you trying to get?  The AW180s are actually great amps with excellent control and nice detail without being too bright.

That being said, you should go with the Pass amp that sounds best to you. That would be a bigger factor than power output based on the size of your listening room.