On point a - some DLNA controllers seem to have trouble knowing where the root of MB's Library is. When I first access it through a new controller, I sometimes have to set the base "directory."
In the HiFiCast app, for example, it's called "Top Level Music Folder" I think it was set to "Media Server->Music" initially, but it had to be set to just "Media Server" and then everything was found fine.
Maybe there's some way to set "Top Level Music Folder" or some similar setting in your AVR.
On the other issue and requesting features and the like, the plugin is sadly no longer supported. You'll either have to learn programming and make a new one (original source code is available!) or find a music manager that does this stuff well.
A smile is happiness you'll find right under your nose.