1/0 would be fine with a 250 or 300a fuse, but u want the fuse to pop if it draws more power than the amps can take. Its the same reason that the amps have an 90 and 40 fuse. U would want a 120a fuse so that if there was extra current spike from the battery it would pop the fuse right next to the battery and not the ones on ur amp. There would be no point for a 250 or 300a fuse if ur max draw is not gonna be more than 130ish anyways.
U can run 2 runs of 4 gauge with no problem. Fuse each line with the max current draw of each amp. So 1 4 gauge wire with a 100 amp fuse, and a 40amp fuse on the 2nd run of 4 gauge.