Retired Mac Pro as HTPC

Hey guys, I need one bit of info. I have search near and far without a definitive answer.

I have a Mac Pro 1,1 w/ ATI 5870 video card...Is there any way via OS X or Windows 7 to pass audio through the Mini Display Port?

Any firmware / EFI hacks, tips, or tricks.

No hypotheticals, I need real-world testimonials. Thanks guys!