yep, I've found cranking the master and then using the gain to set a level on the SVT3 the way to go.
I've now read about the pf500 cutting out on Talkbass which is kinda putting me off, but then many folk seem to be using without any problems, same with the Orange BT. Reliability is a big deal to me, even at the expense of some tone. I want to plug it in and for it to work with no faff or feelings of "will it, won't it??????".
The more i'm thinking about this though, the more I'm feeling moving on from the SVT3 might be the way to go. Given the feedback here I'll check out the PF500 cos it certainly sounds like the sort of thing I'd like, but really I'm not looking specifically for a super lightweight class d amp, just "lighter" with a bit of upper mid bark.