uprade you altenator to a higher amp. upgrade all power and ground wires dealing with the battery,alteranter and your amps . wahtever gauge size wire goes in (+) goes out(-) as well with the same gauge wire. plus a cap. this should be all the thing that need to be done for heavy competition stereos set ups.

but your system isnt that extreme to do all that is listed

 

You don't really need that much for only a 600 watt rated amp. The average power versus time isn't even close to that. A new stock alternator will be fine, and maybe a cap to take the edge off of the transient alternator demand. A good battery is helpful though, the same properties that make a good battery supply power better also make it charge better and can sometimes be more alternator friendly.
You don't need to upgrade your alternator wiring for a stock alternator, it doesn't serve any purpose because it's already large enough for stock output (and the wire length is short).. You're interested in decent battery wiring, so your amps can get the power they want over the distance from the battery to the trunk.