Since you already have the SBZ, that is already above and beyond typical on-board audio and it's no slouch with the Cirrus Logic CS4398-CZZ DAC. I guess you just have to ask yourself how serious you are about listening to music and just music, and weather it will justify a dedicated DAC like the e10k. IMHO the SBZ will more than suffice.
Personally, my PC focus is gaming (as yours sounds like it is also), and all my music listening is done through my Onkyo AVR (which IMHO is just as good if not better than the E10k!)