sorry,I don't understand,you have 0 gauge running to the back and 4 gauge on the amp,what's the 0 gauge running to?Also will 100amp fuse be enough for 0 gauge?
what I mean is that I have 0 gauge wire running to the rear of the car where it goes into a distribution block and then out into two 4 ga wire for both amps. I had all 4 ga running in the car and had the sundown hooked up to straight 4 ga for 3 days with no problems. I still have my 100ANL fuse installed also and it hasnt blown yet. So you should be good with 4ga runs.
youll be fine with 4ga but if you have the chance of getting more power later possibly a 4channel for factory replacements then go with 1/0 ga it will be cheaper in the end and youll only have to do it once .