Excerpt from BM2 forum
When you import a midi file into BM2, the sequences all show up on "Main" tracks. Create a "drum machine" instrument with a suitable preset for your song. Then find the drum sequence from your imported midi file and touch and drag it onto the drum machine instrument in the sequencer. Press play to make sure it's working so far.
Then create an "audio track" instrument. Make sure "monitoring" and "record arm" are selected in the audio track settings and you should be good.