Speaker suggestions for Pass Labs x250?

go to the montana audio site and take a look

Now that's an open ended question. There are many many options at 5 grand. That pass labs amp should drive any load you throw at it without going crazy big. Great preamp and CD player too!

My vote is Matin Logan Vantage if you can pull them out about 3 feet from the back wall.

Dynaudio C1 ($4,500 used).... a robust & very well respected monitor that would be a good fit for your room & equipment.