Help me out on tone - Fuzz/Crunch

[Buzzo]

I'm not sure where to put this, but I am looking for Pedals so I guess it goes here.

I'm starting a Sludge/Doom (tone/speed) and Black (Vocals/Drums/Structure) band, and it's just me out there on bass alongside a vocalist and a drummer.
We've practiced a few times but, I need to improve my tone greatly, what I have now is just a crappy muddy fuzzy tone that all mushes together in the lows (which doesn't work too well because I play in FCGC, but I do mostly chords so It's got an....acceptable effect).
Anyway, for now I'm just running three combo amps together (a Peavey, a Marshall, and a Laney), I don't know the Models so I can't provide that information....My fuzz is natural, no pedals as of yet.

I'm wondering what pedals I could use to get more of a 'crunch' with my fuzz tone, and still keep my low end, I'm really looking into RATs/RAT clones, Metal Muffs, and I was also looking at a Tech21 GT-2. But those are all guitar pedals so I have no idea what they will do to my lows.

The Metal Muff (w/top boost) has been what I've been looking at mostly, it's almost exactly what I want, I just will just work on making it a bit dirtier. But, I'm not sure if that will hold my lows well? Will it?