Ren them off of a fused 12V line from your battery. Use your amp remote wire to turn on a relay...use the output of your relay to turn on the fans and the amps. That's the safest way to go about it.

Runing a push/pull config is a waste of time and money. If your amp rack is really sealed, then you only need fans on the exit or entrance...I like to pull air across. If you have extra money, throw the other fans in there, again waste of money.

If you want more info, go here:
http://www.eatel.net/~amptech/elecdisc/

Some excellent info on relays, fans and ampracks is located there.