Ok figured it out. You have to remove the username/password (which are represented as numbers for some reason) from the url, and add the user/pass (again as numbers, why I have no idea) into the seperate login fields.
That said if anyone is thinking of signing up for Stitcher premium I would recommend a hard NO. The episode descriptions unlike the free official feed for Earwolf shows are unnumbered and dont contain guests in the titles making it near impossible to find what you want.