Nice to hear that you're using the combination of desk control and pixel control for the units. that's exactly why we have the oportunity to set our Node's outputs to merge 2 different ArtNet sources (PixelMad and desk) in either HTP or LTP mode. In LTP mode you can even take control with the desk to flash different colours when you have a still image. With LTP you don't need to bring the PixelMad colours to zero to do this.
Have a look at our Node's app note it shows a similar setup (maybe not mentioning the right pixel software.

Ethernet - DMX8 Application note