I currently run Csound on a Mac, so what I am about to say with regard
to multi-channel output on a PC should be taken with a large amount of
salt. I have _no_ direct experience to provide.

A company called Frontier Design Group (http://www.frontierdesign.com)
offers hardware and driver software that enables multi-channel digital
and analog 16 and 20-bit audio on PCs, at least 8 to 16 tracks worth of
sample-synchronous data. It seems from my reading of their literature
that the driver might just work straight out of the box. And if not,
they seem willing, on virtual paper at least, to provide information
that will allow developers to code for their API.

regards,
-jim