it looks like it was a nice system when it was new. I bet you paid a bunch for it too. unfortunately its 2 or 3 generations behind technologically. I would say maybe $500 tops. the only reusable parts are the case,PSU, DVD and the HDDs as secondary storage. the X-Fi card is cool, but on-board sound has come such a long way the sound cards are now for the Audiophiles only.
I dunno, I'd probably salvage the PSU, sound card, fans, lights, and maybe the case and offset the cost of a new build with those components. They're probably worth more in savings that way than you'd get for selling the machine.