i'm guessing you'll be running this on the 12 V rail?
in that case you'll want to use the DC power equation:
where I and V are your 12v rail specs.
so for my psu that would be P = 12V * 18A which is 216 watts MAX.
your's will probably be higher but nowhere near 600 watts. :roll:
my prediction would be... a burnt PSU
if you crank up the volume on your stereo, or whatever it is that you need 600 watts for.
i think you could do it on 2. Make sure to leave some over head though.