We’d like something more “direct” in the future, so people can contribute corrections and content directly to Roon’s database, but for now this is probably the easiest way to submit albums that none of our providers know about:
http://musicbrainz.org/doc/How_to_Contribute
Just note that we don’t currently use every single field they offer, so I would caution against assuming that everything you submit will automatically show up in Roon.
Interested to hear how this works out if you guys give it a shot – let us know!