I right clicked on an audio track selected Save Audio Track (or selection) as wav/wma/mp4/m4a... this brings up a window drop down to mp3 choose quality and mono if mono track then it saved to mp3.


I soloed the track audio/midi went to Audio menu Merge Tracks to compressed file and it saved to wav first then converted that to an mp3.
Had to have audio driver set to MME to get sound from the midi track Vi in the mp3.

Real band 2014 (7)
I have K-Lite Codec Mega Pack installed 32 and 64