I have the Bass Big Muff and a Stingray peramp in my Jazz copy with MM humbuckers and find that you need to roll the volume and bass back quite a way before playing becasue the fuzz starts to cut out and just your clean signal is passed through. It might just be my bass (as it is homemade and I am intending to remake the preamp as the bass knob acts in a peculiar way) but I have heard similiar reports with the BBM and hot output basses.
If you want a good Muff based fuzz that works well with active basses, I would save and either get the Way Huge Swollen Pickle (which apparantly takes a lot of tweaking) or get a Fuzzrocious Grey Stache + from a dude on here. I love mine and it is basically a Muff on steriods (gain boost and gating on extra footswitches and a mids knob to get rid of the mid-scoop and help you cut through more)
In general, the BBM sounds good on its own, but does tend to get lost in a band setting.
What kind of stuff do you play and what amp are you playing through? The best advice to get on here is to give as much info as to what you circumstances are and what you are trying to acheive as possible
Hope that helps a little
