To be honest, I think the mobo you posted won't be much of an upgrade, in the sense that it will seriously limit your upgrading possibilities down the road. If I were you, I would get a DDR2 board (AM2 if you're on a budget, Conroe if you can afford it) so that you'll have both a nice processor for your money, and the ability to upgrade if you choose to do so. Oh and about the X-Fi, I think for the money the Audigy 4 is a better deal at almost half the price and (correct me if I'm wrong) pretty much the same CPU offload.
OK I did some research and yes, the new P965 and 975X chipsets from intel are backwards compatible so you can use your processor with them. You can also get an NForce 5 series. For what it's worth, the ASUS P5NSLI is a very well equipped motherboard for you money. Hope this helped!