You are right about Openinkpot - it won't read DRM protected files.
When Bebook started out it would only read Mobipocket DRM then at a later date it would handle ADE (Epubs) and had to drop the Mobipocket. I can't recall if when it got ADE it could handle PDFs though.
There was some firmware by Tirwal that allowed booting to either DRM scheme - most sources of this were Italian IIRC but you might find something that still works by searching for that. Have a look at
http://www.lectoreselectronicos.com/...read.php?2712-[FIRMWARE]-Tirwal-2-9-TRIPLE-BOOT-ADDONS for instance (you might need to get Google to translate it for you).
The Italian Papyre reader was the same hardware as the BeBook and I've used Tirwal firmware on a BB 1, though I'm not sure where the instructions are any more to get it to boot into the right configuration.
BobC