Computer output to DAC, which route?

I have disbanded my main system because I am using my computer system more and more. I am going to purchase an outboard DAC for my computer, but I want to know something:
My computer comes equipped with COAX and TOSLINK outputs on the motherboard. Should I use one of those or use a DAC with a USB connection? WHat are the pluses and minuses of each way if any? I am using typical Altec Lansing speakers (good for what they are) but will probably move up to active Dynaudio monitors in the future. All music is sourced from itunes in either AAC or apple lossless formats.

Thanks in advance!