i love my tube preamp with my class D monoblocks. i haven't heard loads of gear, but the tube pre seems to add that bit of warmth and a sense of the sound being tangible that may be missing with straight class D amps. though i really should try them with a passive pre, just to hear their true nature..
i'm running ghent audio monoblocks, which apparently use 2 ICEpower ASP modules in each amp putting out 500w/channel into my 4ohm floorstanders. the preamp is a modest dared mc7-p.
the build quality of the amps is very solid. excellent cmc binding posts and rca jacks, solid housing.. and the sound! my speakers have side firing 12" woofers and these amps control those drivers like it's their job. because it is. but they do it well and with authority. the separation of sounds is equally incredible and i'm constantly amazed at the raw power my ghents deliver along with delicate detail effortlessly floating on top.
good stuff!