We would really like to run this through XenForo if possible and i was wondering if there's anyway to have pages restricted to user groups allowed us to use user upgrades for theme purchases with download available on a page?
If there's another way within XenForo this sounds possible that would also be great.
Not directly. Page nodes can't contain attachments, but forum nodes can. You can create a forum node underneath your page node and post the attachment in there. Then you can link to the attachment in the page node if you want. With the forum as a child of the page node it will inherit any custom permissions you set for the page node.