I can't comment on the TH500 but I recently purchased a new Puma 500. It's the best amp I've ever played through. My Rob Allen Solid 4 and MB-2 both sound really great through the Puma.
EDIT: In fact, they've never sounded better!
+1 With the Rob Allen basses, which have that very wide, buffered piezo tone footprint (i.e., massive sub bass and very sizzly, aggressive treble), the newer Puma amps like the one space Puma500, work particularly well.
The shelving bass control with that super low starting point works almost like a hi pass filter to control the sub-bass of the Allens, and the very high shelving start point treble control acts quite a bit like a lo pass for the sizzly top end (although that can be adjusted through the hole in the control cavity cover on the Allen's).
Even more importantly, the Puma's low mid control is perfect of adding a fat, round low end, and the upper mid control is nice for addding that 'woody complexiy' that makes the Rob Allens sounds quite a bit like a DB.
Finally, the taste filter, turned counterclockwise (if I remember right) is like a 'reverse scoop control', rolling off deep low end and treble and bringing out the mid mids, and was specifically designed to bring out the woody warmth of a fretless instrument.
Perfect match with the Rob Allen. The TH500 sounds good too, but I found that you need a bit more help with cab matching to really make that work with the Rob Allen. A cab with nice midrange response and a tight, non overextended low end and the TH500 can sound really nice and warm and organic, even more than the Puma, but you have to work at it a bit.