Yes i’ve worked on C4 in the past and had displays running fine using our own applications, the trick was to send the correct SysEx message to address the C4 (And not the MCU).
I wish i had a C4 here, or at least a working emulation so i could help you more.
In BOME MTP, my idea is just theory but it should work as you would have the following virtual ports which Cubase SENDS to for each MCU setup:-
Mackie 1 = VIRTUALMIDI1 (VM1),
Mackie 2 = VIRTUALMIDI2 (VM2)
Mackie 3 = VIRTUALMIDI3 (VM3)
Mackie 4 = VIRTUALMIDI4 (VM4)
And you just ensure that device ‘10’ is replaced by ‘17’ on all the incoming SysEX’s, and that row 10 is replaced by 30/31/32/33 respectively for each row.
VM1
Would Convert
F0 00 00 66 10 12 xx xx xx xx xx xx F7
To
F0 00 00 66 17 30 xx xx xx xx xx xx F7
VM2
Would Convert
F0 00 00 66 10 12 xx xx xx xx xx xx F7
To
F0 00 00 66 17 31 xx xx xx xx xx xx F7
VM3
Would Convert
F0 00 00 66 10 12 xx xx xx xx xx xx F7
To
F0 00 00 66 17 32 xx xx xx xx xx xx F7
VM4
Would Convert
F0 00 00 66 10 12 xx xx xx xx xx xx F7
To
F0 00 00 66 17 33 xx xx xx xx xx xx F7
Using MTP you would take those 4 filters, and then pass it to the C4 hardware, and ensure that the MCU’s are placed in the correct 1-4 order in Cubase to get the rows in the correct order. I believe you have to connect the last one first, so you would assign them VM4, VM3, VM2, VM1 etc.
That would be your initial starting point at getting the display to work.