Actually, my Bloc 40B is just a 10" speaker, 40 watts. On the way home from work today I actually rented one of the DB50s, I have it for a month for $15!

I tried it out, and it actually sounds remarkably similar to my old Bloc 40B.
I picked my 40B up from the repair today too - they didn't actually repair it, as they said parts are no longer available, but I tried it out at home alongside the DB50, and it is remarkable, the similarity.
The break up I'd been hearing is still there, it kinda sounds like it is being pushed hard or something, although the volume is only at 3:00, and my bass is a passive P bass. Maybe I'll try it out plugged into the Low input to see if that makes any difference.
The DB50 breaks up anywhere past half volume, but as this will not be my gigging rig (!) it should be ok - more available volume than my 40B, I think, but my ears could be playing tricks.
So I'll hang onto the DB50 for a month, play with the features and see if I can like it enough to pay for it, or if I should go cheap and try harder to figure out what is wrong with the 40B.
I've been leaving my gig rig at the drummer's house the last couple of weeks, and at 500 watts it's actually hard to get it to play quietly, so I do need a practice amp. iPod inputs and headphones out make it an attractive solution, just concerned about the Chinese fabrication.
Rev - I don't know if you're allowed to comment or not, but if so, do you have any comments on QC or returns from these Chinese units?