Euhm… what ? You’re asking to merge midi-tracks en audio parts ?
Midi = musical data
Audio = what you hear
You can’t merge those… Why would you want that ? :S
+1 on the mono/stereo feature though. I hate to receive 2x mono files, make a group channel, pan 1 mono track left, pan 1 mono track right, route to group channel and use batch export. This is just a silly way of working with audio.