I'm currently using a Xonar STX, if it matters.
I would agree with jwjw, I have the PC166 and while the microphone is decent, it doesn't compare to some of the clip on mics I've used. The buyer pays a premium for the integrated microphone and the audio quality usually isn't as good compared to purchasing a separate headphone and mic for the same price. However, I should also mention that I have never owned/heard the PC350. From what I understand, the PC350 shares the same driver as the HD555, which isn't a terrible headphone by any means. If you can pick up the PC350 at a low cost, it could be the perfect solution for you.