I'm using an Odyssey Khartago SE with an Odyssey Candela tube preamp with a pair of M100s. Sounds GREAT.
Matt, not to start a discussion which could wake this place up, but my experience with tube amps is that they produce excellent sound quality. If you audition a good tube amp, or even a modest tube amp like Monoprice's $150 effort, you might agree that the difference is not "distortion." To my ears, tubes sound more "you are there," more like real life. It may be that the tube sound does not add "sweetness" as much as solid state amps miss it.
Personally, I think that tubes in the signal path improve sound quality. [Don't know about tube buffer stages]