I have D9s and have used them with X250.8, XA30.8, Benchmark AHB2, Bryston 4B3, and AtmaSphere Class D monos. I've enjoyed them greatly with each amp, including the Benchmark which has a different sound signature than the others.
My listening room is small (12ishx17ish) and I never once got the 250.8 to leave its class A bias, so thus the switch to the cheaper 30.8. If I was in a large room I would likely stick with the 250.8 between those two, but I do like the extra midrange magic and soundstage depth I think I hear with the XA amp. The 4B3 was a great match with them too and I think offered the best bass in my room of any amps on that list.
The only two amps I still own are the 30.8 and AtmaSphere. Definitely checkout the AtmaSphere monos if you get a chance.
Cheers