Henry - They do indeed. Also, USB 1 doesn't offer huge amounts of bandwidth, and you could well quickly run into contention issues. Best to go for some sort of PCI card imo.
With regard to optical vs coax, the traditional hifi wisdom is that coax is better. Fair enough, but it is worth considering that computers generate absolutely huge amounts of rfi, with the number of clocks in there, motors, switch mode power supply, etc, etc, etc... If you use a coax to connect this to a piece of hifi, you've just given the rfi a nice conduit straight into your hifi. Using an optical lead prevents this from happening. Swings and roundabouts for sure (and the reason I use an optical is because that's what my aureon has out, and I use the coax in on the DAC for the cdp), but something to consider.