My thoughts:
Why let your current music collection limit your future?
You'll get more music eventually, and with larger discs you'll want higher quality files.
Also, don't choose a DAC that can only be used with your current PC. Your next laptop will have an optical output.
USB is (except for a couple of expensive DACs) limited to 16bit/48kHz. Many high quality music files available at net shops are 24bit/96kHz. Also, an optical cable isolates your PC from your hi-fi system, eliminating potential ground and noise problems.
Beware that some inexpenisve DACs also has the 16/48 limitation on optical input. As far as I know, neither the DacMagic nor the Beresfords have this limitation (but I can be wrong).
Unless you want to be stuck with your PC as your only music source, you should also choose a DAC with separate inputs and a switch for choosing between them. It's very annoying having to switch cables every time you want to listen to another source.
Sony / Apple / Rega / AVI