Coaxial Digital Out

Google it. Optical to Coaxial Digital converter for the Mac Pro....... or something along those lines. Personally, I would check with the manufacturer of yor D/A converter for options. If it's high-end, computer quality parts will downgrade the sound quality. JMHO.

Michael

You can use this http://www.m-audio.com/products/en_us/CO2-main.html
if you want really hi-end Apogee Rosetta 200 can serve as a format converter but this would be overkill

You could see if you could find one of these:

http://www.amazon.com/M-Audio-Sonica-Theater-24-Bit-Surround/dp/B00009L7N9

which does firewire to digital coax, or find a compatable PCIe sound card with a digital coax.

why would you prefer coax over optical. Coax introduces noise into a signal. as optical does not at all

He doesn't have an optical input on his converter.

Coax carrying digital isn't an issue like coax carrying analog. When you push digital audio data over coax, it either gets there, or it doesn't. The data is binary, not analog, so the noise doesn't matter. I prefer fibre, since it removes the potential for ground loops.

noise does affct the signal in coax digital or not. it will add artifacts that can harm the square waves used to carry the binary signal. in many cases rounding them off. this happens especialy with coax over distance anything over 3 feet is not generally acceptable (in the pro world) wich is why we all prefer either fibre optic or balanced signals. Such as AES/EBU.

it will harm the square waves, but they'll either turn into 1 or 0 at the other end, nothing in between.

AC3 and PCM include a degree of error correction, which should fix this, but if it doesn't, you'll lose data, and therefore sound, which will be noticable.