Preamp to go with a Pass Labs X250 ?

I would keep in the Pass Labs line of preamps. Also consider Klyne as well as Jeff Rowland. If you plan to play vinyl, then the Klyne is my overall choice.

Usually tube preamps do not match well with Nelson Pass designed gear. There much better matched for solid state.

The X-1 is a neutral sounding preamp and will not add the tube sound that you mention. The best preamp that I have heard with the X-250 was the Tom Evans Vibe (without the upgraded power supply), it smoked all the others that I tried (12 in total). I also would consider the new version of the H-Cat, as I hear it may be better then the Vibe but have not heard one myself.

Ferrari, I don't know where you heard that the Pass gear does not work with tube preamps, that is just plain wrong. I have used many with the X-250 and even the passive Sonic Euphoria preamp worked very well with the X-250.

Do a search this has been covered before.

Happy Listening.

Finally discuss with Nelson Pass - Nuff said.