If you can afford it, I think the best option would be just get another 480 to double performance, that also has an HDMI output on it.
The 480's should support audio bitstreaming, meaning it can carry audio through HDMI without needing to connect a SPDIF cable to your card from your mobo.
Missed it since it's a mini HDMI on the end.
I'm still a bit tempted to get another GPU and SLI, but I'd get a 580 over a 480, and more than that, I'll probably wait until the 6 series now...
I'll keep an eye on ebay in case any nice physics cards pop up for cheap, I have a good idea what to look for now at least ^-^
One more question though, for PhysX, do you need to run that with an SLI bridge still?