But everything is fused, the three power feeds are fused close to the battery terminal with inline blade fuse holders, 1 is a 3AMP fuse for the Empeg power line, and the other 2 are 30AMP fused for both Alpine amplifiers.

The requirement of a Fuse block was to reduce the number of wires going to the battery.
I'll run 4AWG wire from the battery and then use my existing 8AWG from the fuse block to the amps, I'll leave the empeg power feed.
However should I use a fuse for the 4AWG power wire from the battery terminal to the fuse block? if so what rating?

JaBZ