each one of those amps puts out 500 watts. they are a class d design, and that makes them pretty effecient, so we can assume the maximum draw from the elctrical system will be around 650 watts per amp, for a total of about 1300 watts in all. now we need to know what kind of amperage will be drawn through the wire. 1300/13 volts = 100 amps. so you need a wire that can accomidate that. referencing my handy MECP wire giude, it states that for an acceptable (.5 volt or less) voltage drop, you should use 2 guage wire for both amps.
heres the truth though...you never going to draw 100 amps from the electrical system. id be surprised if it reached 70 while listening to music. the only way you will ever reach that number is by playing sine waves at full blast with the gains turned all the way up. im assuming you dont compete in db drag or any other form of SPL compitition, so youll never have to worry about this. 4 guage splitting off to two 8 guage wires will be fine, however make sure they are fused with 40-50 amp fuses per amp at the distrobution block and make sure you keep the run of 8 guage to a minimum. naturally youll want to fuse the 4 guage wire at the battery at 100 amps, but im sure you know this already (i hope!). you might want to look around online for distrobution blocks that can both accept and distibute 4 guage wire. if you go that route, you will not need to fuse the wire at the distrobution block (in other words, you could buy a "ground" distrobution block and use it for power). the reasoning is this: you only fuse at the source of power or when the wire guage decreases. since the primary wire will already be fused, and you dont step down in guage size, you wont have to re-fuse anything. plus you wouldnt have to worry about increased resistance and voltage drop because of the 8 guage (although it would be VERY minimul assuming you kept them under 20" in length or so).
ok, thats much more than i meant to write, lol. if you have anymore questions please ask.
