Planning on buying the XW8200 workstation for Avid Xpress Pro HD, I was wondering if I need to buy a soundcard, let's say a soundblaster Audigy, since I work with Mojo? Because sounds go through Mojo for monitoring and output.
Not necessarily, no. I believe that the XW8200 even has a pretty decent on-board sound controller that you can use for apps outside of Avid, so the Audigy would just be a bonus and you'd have to determine if it's worth it to you.