Do you want to find out what's currently there on your board (if thats the question I think all DR31PR series boards come with the realtek chip. You can take a SPDIF output from the MB
If you are looking for an audio card for your PC let us know your budget, level of usage (just listening to MP3 or would you go for a PC based studio later? do you want connect keyboards/synths, etc for midi control?)
Get an Asus Xonar DX. Since you are gonna use digital, internal converters don't matter and that asus card will do the job. What motherboard do you use btw? If it has an spdif out, you can just use that though quality will be sub par due to 48kHz resampling.