Hi Charlie,
I am not using two instances of BiaB and I am working entirely in Midi. I don't find that I can use BiaB to search for styles that have a Midi drum track.

I identify a particular drum track from a selected style that suits my purpose. Once I have the track I want I then disable Realdrums in BiaB. This will result in original Midi track for drums.
The midi track can be inspected in the Piano roll and if Channel 10 is selected I can confirm the mapping of the drums (GM).
The midi is dragged on to an Ableton track on wich is a GM mapped drum kit. This will allow the audition of the drums. I can now edit the midi and save it in midi, if necessary (for re-importing into BiaB, but this is not the intention.

My original question was to ask how others are working with BiaB midi drum to achieve a similar reult.