Maybe it's because yours is a series 2 and mine a series 1, but I find the Mudbucker (which changed from S1 to II, as did the electronics and position of the pup) really gives tube preamps a hard time - requires a rumble filter at least. SS preamps don't sweat it half as much, I find. I think these just really benefit from a big rig that can reproduce what they dish out properly, and possibly tube power sections to add some harmonic content to fill out the upper midrange a bit.
Anyway, its great that that worked out for you.