Forget HDMI, and get a great subwoofer instead. You will hear an improvement with every source that has bass, not just new audio formats. I personally would go with an SVS PC-Ultra, but there are other good choices.
If you must have HDMI, the Yamaha RX-V663 is tough to beat for price-to-performance ratio, and that would leave you with enough to buy a decent subwoofer (but sadly, not the SVS PC-Ultra).