I can insert a midi instrument into one track,  then put another in the second track.  So far, I can only record one at a time with the keyboard.  Then you can play back all or mute some as needed. 

Mentioning Reaper,  you can add several tracks as above,  and be able to play all combined to give a needed effect.  (Or mute those not needed to record with) 

Is there a setting in MMM to allow more than one track to be recorded and monitored at the same time?