Hi Goon,
To add what support said above, the choice is yours with that digital/optical I/O. If you wanted to hook up your CD/DVD player you would choose the SPDIF mode and input music that way. Or, if you had another AD/DA with optical ins and outs, you would select ADAT and then have up to 8 channels of digital I/O, depending on the resolution you want to work with. Higher sampling rates than 48K would use SMUX and then you'd only get 4 ins/outs.
I haven't looked at any mixers with optical I/O capability but I believe what most folks do is get an 8 channel A/D/A converter like the Ferrofish of BehringerAD8000(?) and connect via ADAT. I have an Apogee AD8000 hooked up this way to the BBF Pro Fs and it works very well.
Good luck
-Steve