Without having to use 2 instances of Biab you could have a Media Browser that you can drag and drop the whole item or a section of it into the Biab track non destructively fitting to the track tempo.
When browsing a RealDrum file it should show the txt file section names above, in or below the waveform in the Media Browser, once the track is made up how you like you can have an option to import those if available Stem sections. This will be a very quick way to create just the drum track you need.
Same deal with Loops you need to be able to drag n drop these (that's going way back, I think old solidrock posted that when he was young and keen smile ), with all the loop options fit to key or chord being able to drag out to repeat, stretch out/in for half/double time.
How it all works now with numbers and names is from the DOS days, you need the visuals.
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https://stash.reaper.fm/u/ReaTrak (Scripts for Biab Reaper)
Open SGU in Reaper Instantly