Well I tried my bass through the guitar board (below), and found the Fullbore Metal surprisingly useful. It's not nearly as fizzy with my bass as it is with the single bridge humbucker guitar it usually has put through it.
The Megalith Delta is too fuzzy with the bass, strangely enough, since it is grindier on guitar than the FBM is. Oh well, different instruments I guess, different frequency responses.
I'm not about to put a Fullbore on the bass board though, as the TFR and Bluebeard do that thing already, and in three different flavors.
I'm saving my pennies for a Mountainking Megalith and/or a Wampler Triple Wreck, though I have my suspicions the Wreck won't work either as demos make it sound a lot like the Megalith Delta, on treble guitar anyway. Megaliths....
I'm convinced this sound I'm looking for will be found with combining distortion/drive/eq pedals with careful amp (preamp section) adjustments. The Mesa M9 has a 5 section preset knob for eq'ing (plus a parametric eq and separate graphic eq channel). I've found that position 2, which is a lowmid hump setting works best for pulling boulders out of distortion pedals. I was using position 4 which is a mid hump, which though awesome with fuzzes (screaming harmonics), was not so good for bouldering.
For now, (since I'm broke for a while and will be using my current board for a project over the next few months) I'm going to experiment more with the B3K/Submarine/amp combo to see what I can come up with. I don't think fuzz is the answer to this puzzle.
Thanks again everyone for contributing. It's totally apparent that similar effects yield different results with different gear. I knew this already, but this thread is teaching me again. Must be an important lesson...
So far, I've tried or am trying
Mastotron
team awesome! fuzz machine
Bluebeard
Unpleasant Surprise
Tall Font Russian
Frequency~LSD
El Oso
B3K
Megalith Delta
Timmy
Monarch
And Aardvarks!
Lomenzo Hyperdrive - so close though, maybe I should get another one...
SexDrive
Rat Tail
The Elements
HM-2
Classic Distortion
Dirty Bomb
Still going to try
Mountainking Megalith
Wampler Triplewreck
EBS Metaldrive - most likely next to try out, since I can get one, try it, and return it if I don't like it. I don't usually like to do that, but it's been a awhile, so....