jonandfamily...
I'm currently using a Simaudio integrated with my 3.6's and find it pretty damn good, 200 watts into their 4ohm load. I sold off my second X150.5 and a BAT VK3i preamp simply because I grew weary of all the wires and what not.
I started out with a First Watt M2(?) ss amp and almost immediately moved to my first X150.5 when I got my first pair of 3.5's. I've had a few AR preamps and they pair exceptionally with Pass and Thiel. The X250 for sale here is an early model, followed by the 250.5, and the 250.8. From what I've discovered, at least with the 150 series, there is no manufacturer upgrade path from one to the next. Obviously, Pass commands a pretty steep entrance fee - the 250 for sale here is as much as a used X150.5 goes for currently, but with a LOT MORE power on tap.
Yes, I'd say the Pass 250 is more than well suited to your 3.6's.