Firstly, it's DRM, not DMR. Secondly, Sony does use an implementation of
Marlin DRM, which was designed to be compatible across vendors and devices. The problem is that none of the other ebook vendors implements it so you can't exactly convert your books to anything else. Also, even if you succeed in transferring your license, it's unlikely the other device will not understand BBeB format...
I, for one, hope that efforts of Baen and TOR will make DRM obsolete.