Finally got this issue FULLY resolved after several calls with comcast. Now I am able to access HBO content on HBOGO.com without being redirected to xfinity's (terrible) website.
Comcast was able to restore my HBO priveliges several times by resetting something, but it continually came back as an issue. It seems that this issue might have been caused by changing user names and/or passwords for my account.
As far as the redirecting problem, this seems to be linked to not having a proper "set top box" linked to my account. I had downgraded to one of the small adapters because i wasn't using it anyway and the large box took up too much space. I stopped by a comcast service center and picked up a regular set top box, which apparently is what allows you to access video on demand services.
Once that was activated on my account, everything worked as before.
Hope this helps solve this frustrating situation for others.