I'm quite familiar with your amps, having heard them on numerous ocassions with 8 different preamps and 4 different speakers (Alon, Audio Physics, B&W, and Revel). I own a pair of VTL MB 125, so I have a good handle on what synergestically matches with VTL stuff.
I'll only rate preamps (1 being bad and 5 excellent) that I heard with the MB250's. Recommendations of other good gear don't make sense to me, since I heard these with your amps:
1)CAT SL 1 MK III- 5 head and shoulders the best completely obliterated a 10K Krell solid state and the VTL 5.5.
2) Hovland HP100- 5 another very good match- not quite as good as I remember the CAT, but it was in a different system
3) CJ Premier 17- 4- Very good. Gave a slightly more musical sound with the VTL's than the above two, though not quite as detailed.
4) CJ Premier 14- 3.5- very good, though not quite up to the Premier 17 level with the VTL's
5) VTL 5.5- 3 - good all around, but really didn't excel at anything and juxtaposed against the CAT, what sounded "pretty good" became "inadequate."
6) Some 10K Krell solid state- 2- great bass, but way too analytical for me. Bad match.
7) Sonic Frontiers- Line 2- 4- Very neutral and seemed to just let the VTL's work their magic. An excellent match, though I'm not sure about service now.

Jadis JP80MKII- 4.5- UNBELIEVABLE on classical- ridiculous tonal color, air, and 3-d imaging. Sounds more tonally correct than any preamp I've heard for playing acoustic instruments and classical. ABSOLUTELY a TERRIBLE preamp for rock, so take note. But if you are into classical, this is the best I've heard with the VTL's.
There you go.
Michael