That's a bad ass tone! I'm not into that style much but I love the mean bad tone going on. One thing I found and it took sometime as my experience got better, is eq starting at the the amp. Pull out some of the low mid (mud frequencies) right around 250hz. Tends to tighten things up a bit. I run a 31band eq in the loop of my amps. Now this is the real trick, get the biggest strings you can possibly stand to play. The reason is, the bigger strings won't flap around at those lower tunings like thinner strings will. Thinner strings will flap uncontrollable at low tunings, snapping at the frets, buzz, go out of tune and all that happy stuff. The pick ups will actually pick up that flap and it sounds like mud going through the amp. All the buzz and flap just smears the sound masking the clarity/tightness; sounds like mud to us. You got to be some gorilla to get big strings to flap like that. I use thick(low e at .60) strings on my paul for down tunnings like that and regular strings for standard tunings. Of course you will have to redo the setup on your bass.
