yeah but that built in fuse is to protect the wire from shorting. do the amps have a built in fuse on them? the amps should say what size fuse they need. what you do is have a main fuse by the battery, a wiring kit shoud come with one. ususally 4 gauge comes with a 60 amp fuse. then when you split it into two 8 gauge wires to go to the two amps, you use a fused splitter, and i'd put fuses there at whatever your amps are rated at.
yeah. the main fuse is at the battery. this is so if your wire gets cut or melts or scraped somewhere, it would short and without a fuse at the battery, the battery would short out and probably explode or catch fire or something. the idea is to use a fuse that prevents more current than the wire can handle. the fused splitter i would use fuses that match the amp's fuse rating to protect your amps. its probably 20 to 30 amps each. if they're more than 30 each than your main will have to be more than 60 probably since you add them up to get the main fuse size.
however you can often use fuses smaller than what the amp calls for. that is because fuses can go over their max load without blowing. its just how much over and for how long that determines if they blow. for instance i have amps that say use a 40 amp fuse and i use 30 amp fuses and it has never blown. i think this would help protect the amp even more if you can get away with it.