That sounds interesting - your code would have to be able to run in a 256-byte block or else be spread across different areas.
A fully populated MK14 has three spaced out areas of memory.
256 bytes of undedicated memory at 0B00-0BFF
256 bytes of mostly undedicated memory at 0F00-0FFF, however the monitor uses 0F00-0F11 and writing to the very highest address 0FFF can do odd things like affecting the flags.
128 bytes of undedicated memory at 0880-08FF.
Given the above, if you need more than 256 bytes then it might be best to put the midi-out subroutine at 0880-> and the main program code which calls it at 0B00->
Intel Hex is actually the best file format for me because I use this project to load code into the MK14.
https://www.vintage-radio.net/forum/...d.php?t=151851
There is a link to a video showing it working in post #17 of that thread.
You can split the code across the various blocks of memory by placing ORGs at strategic points in your source code and the uploader will send it to the right places.
It's kind of you to offer to do this, but I should say there is no rush because I am about to go away for the long weekend - hopefully should have a chance to play when I get back.