While it would be great for this to be implemented in JRiver eventually, I have found a workaround. When a download completes in my torrent client (Deluge), SickGear copies it to my media library folder and now runs a script afterwards which tells mkvpropedit.exe to remove the Title field from the MKV file. This happens fast enough that it's done before JRiver sees the file for import. Only drawback is a cmd window flashes over whatever else you may be doing for a second whenever the script runs.
Here's how to set it up on Windows:
1. I'm using SickGear for download automation. I did not try this with SickRage, SickBeard, or Sonarr, but they should work too.
2. Install MKVToolNix if you don't already have it. This gives you mkvpropedit.exe.
3. Create a batch file script. My script contains one line, including the quotation marks. Modify it to wherever mkvpropedit.exe is located. SickGear passes several arguments to the script. 1 = final full episode file path. "C:\Program Files\MKVToolNix\mkvpropedit.exe" %1 -d title
4. Save the batch file in the C:\SickGear folder. Or put it in the Data folder if that exists. Wherever sickbeard.db and config.ini are, that's where the script should go. Mine is saved as RemoveTitle.bat.
5. In SickGear, go to Post Processing options and find the Extra Scripts field. Enter "RemoveTitle.bat" without the quotes and click Save.
Now the batch file script is run immediately after the file is moved or copied, removing the Title field and forcing JRiver to rely on TheTVdb to get the episode name.