@dogs: anywhere from "hmm that was kind of expensive" to "oh man....I spent way too much money". I guess all it would take would be getting the appropriate receiver (one that supports 7.1 channels of audio through HDMI, I don't know how much the cheapest one is these days) and a full set of 7 speakers (these vary in price greatly...)
Warhawk sounds awesome though. It has the best sound effects of any PS3 game that I've heard.