Hi Max,
my solution is too specific to make it a product. (i.e. amount of support vs. amount of money to be made)
You might actually get way with just splitting the raw MIDI to both modules.
MIDI is a current loop signal driving an optocoupler (think of a LED that blinks) if you split passively the current might not be enough to drive all “LEDs”. Two modules might be ok tho.
You are also lucky cos both modules expect this current loop… some modules (including mine) expect a serial logic signal, so you couldn’t do just that.
The only difficulty for you is to find the correct pins.
Os also publishes his pin out in the module manuals btw.