I think RipX would be good to adjust the stereo RealDrums individual levels by the demo I saw of it, so it will give more control than Spleeter.

Reaper can do more than split a stereo track:
Extract Drums Bass Vocals etc.. from songs with Spleeter in Reaper
https://www.dropbox.com/s/109uinkzbbaaqde/Spleeter-Reaper.mp4?dl=0