Don't create separate Libraries for a simple thing like this. In fact, there is almost no good reason to ever create separate libraries with Media Center. Don't do it. Put everything in one library. MC can handle it all, with tags, views, etc.
For your viewing pleasure, simply set MadVR correctly. Actually, have you imported and tried playing these files yet? Do that first, and see if MC does exactly what you want by default.
If not, go into Options > Video > General Video Settings > Open madVR Settings (Advanced)... > Processing > zoom control
Tick "automatically detect hard coded black bars"
Play the videos and see if MC now does what you want. For me that is enough, along with "keep bars visible if they contain subtitles". If not, play with the settings found in "zoom control" to get what you want.
Oh, in case you didn't get the message the first time, do not create separate libraries for JRiver Media Center. If you need to do something that you think requires separate libraries, come to the forum and ask first. It will save you a lot of pain and work.