As mentioned... It is a HIGH priority that the Negative be the same, if not larger gauge. If you're running 2 amps, I suggest running a 2 gauge cable to the back of the car... a distribution block at the boot, and 2 x 4 gauge cables off that. Get a 4 channel to run the speakers... at least 70w RMS from each speaker, and make sure the speakers are at the same spec. You're best off running a sub or two off a Monoblock amp my friend. See if you can get a hold of a 300w RMS Monoblock (1 channel) if you're wanting to run just one sub, or maybe a 500w RMS monoblock if you're wanting to run 2 x subs. Get 2 x 250w RMS subs on a 500w Monoblock, and connect them in the same connections on the amp... it'll haul ***** mate! 1 - Only talk in RMS language... lol... I don't know the wole PMPO thing, coz that's what I call "bullsh!t power". You can't just half the PMPO rating, because it's still not 100% correct for the RMS power. All in all... 1 x 4 channel amp running speakers... 70w RMS each channel or better 1 x 500w RMS Monoblock... connect 2 x 250w RMS subs (12 inch is good). The monoblocks these days are 2 ohm stable anyway. My 2c :)