Suitable tube preamp for pass labs x250

When I had my Pass 250.5 I used it with a Thor TA-1000, absolutely superb match.

I would pay attention to what Tvad said. Great preamps won't sound so good if not matched properly with the input impedance of the amp. One fine tube preamp that can qualify would be the Joule LA150-MKii with the MU follower engaged (400 ohm output impedance set like that), should be able to drive most any load. Though it does not run balanced. THe Atma-sphere MP-3 is also quite good, but I'm not sure what the output impedance is - I think it is 600 ohms, which should work fine.

I used a Cary SLP-05 with my Pass Labs X350.5 Amp and the combo was not good.
There was limted frequencey on the ends and low dynamics.

Suggest going to a Pass Labs Preamp.

Used all of these preamps on my X150.

In order of what I think worked best - all preamps worked well.

1. Supratek Chardonney (more tubey sounding warmer deeper bass) no longer made though.
2. Modwright SWL9.0 (better soundstage more focused sound more prominent treble though not bright, clean , but not tubey sounding)
3. Belles 28A (best tightest bass most extended, great soundstage, harmonically a little thin, great remote control)
4. Joule LA100mkIII - (warmest of all above and not as refined though this is Joules older preamp the newer LA150 , is supposed to sound similiar to Modwright)

Given that you have the X250 and not the X250.5 which is suppose to be warmer, I'd go with a warmer fuller sounding preamp. I'd check out the Modwright (even the 36.5) with tube rectfication (though it is not a tubey sounding preamp it is not thin). A newer Joule the Cary 05 is suppose to be tremendous. Abe Collins used it with his X150 and he loved that combo.