When a midi instrument is converted to audio let that audio track be moved to the BIAB display Screen.
There is room in the black portion of the screen. The midi track converted could be deleted and
allow another instrument to be inserted.

It would also let one use the audio features such as reverb to enhance the audio. And it would also allow for more instruments to be used in a selection . Infact this the moving of Realtracts to the locations could also be done to free up the instrument Realtracks to allow for more instruments.

In conclusion, this process would allow for more instruments in an arrangement and make it possible to enhance the audio with various plugin such as tone, revert. etc.