As Ultramix seems to use midi standard for computer communication in theory Ctrlr would be suitable. You would need a sysex implementation chart from Mackie to know how midi messages are built up (probably sysex). If Mackie does not provide this information you would have to reverse engineer it. This could be feasible if sysex is not too complex but you will need knowledge about midi, sysex, ctrlr and maybe Lua (the used programming language of Ctrlr).
Offtopic: you are using cheap Behringer AD-converters? They will only do 48khz sampling rate which will limit soundquality significantly. At least to my ears a good ADC with 96khz samplerate will make a big difference. Also vst-plugins will sound that much better when the DAW-Project is set at 96khz. E.g. there are very good master-tape simulations to get the punch of an expensive tape machine. Even at 96khz you may still hear a difference to real hardware but I would say that it gets damn close.
Of course, to make a CD you then have to downsample to 16Bit-44.1khz which is an art of it’s own.
