Yes, kind of. There is an IC that is dedicated to maintaining the MOST bus interface. Its sole job is to receive data from units further up the chain, process any information it needs and then create the MOST bus data containing the digital audio.
The audio chip has two inputs, left and right. The chip needs to be controlled externally by a processor. The IC is designed such that when the LRCLK is low audio from the left is converted to digital, and when high audio from the right channel is converted to digital. This would happen very quickly.
The problem is the right channel has been intentionally pulled to GND with a resistor, this must mean that any information from the right channel will be ignored otherwise audio would only come out of the left speakers in the car.
It could therefore me assumed that the LRCLK could also be tied to one logic level as the system as a whole only processes left channel data from the IC. But.... That input goes off somewhere, it's a 4 layer board with power planes on layers 1 and 4 meaning you cannot visually trace the tracking.
I understand what you want to do, it may be worth looking at the factory DVD changer wiring, I'm 99% sure aux audio and video is routed through the video module. That may only be applicable for the 5drive tuner for rear entertainment. However the PCB looks to have provision for another two tuner modules like the 5drive. I may take the tuner apart and investigate the card more. It would then be a simple task of recoding the MMI to add DVD functionality.
Hope this helps