Hadn't even occurred to me that it could be a problem with the Roku itself. Do you happen to have any sources that enforce HDCP on an HDMI output? A Blu Ray player would be a good way to test this out. If it works just fine then you'll be spending extra money to get something to work when you shouldn't have to.
LOL, I have a Blue Ray player, but no disks to play. It was a gift last year, never got around to hooking it up. Don't like buying or renting movies.