Wormhole, I just read this entire thread and I want to make sure that you understand the sizing basis for the fuse that goes between the auxillary block and the battery (even though many have already said this). The fuse needs to be smaller than the rating for the wire that you use. The only purpose for that fuse is to keep the wire from burning in case of a short. You asked about 6 gauge wire. 6 gauge is not rated for 100 Amps. Again, the fuse needs to be sized for the connecting wire, not for the ultimate load on the fuse block. The fuses in the fuse block protect all the wiring downstream of the fuse block.

FWIW, I installed that same fuse block on my firewall. I used less than 3' of 6 gauge wire with an 80 amp fuse. I haven't look at a chart but you would need 2 or maybe 4 gauge wire for a short run protected by a 100 amp fuse.

Good luck with the wiring.