The Macronix DAC chips aren't programmable in any way, they are ASICs (Application-Specific IC).
Their function is built right onto the silicon, there's no Flash / EEPROM / ROM or anything to read.
A replacement DAC could be built using a cheap CPLD and an RGB / YPrPb opamp though.
I haven't done anything on this in months, but I still have the code for interfacing to a GC / Wii / N64 DAC.
I was hoping Marshall or somebody would come through with a new DVI / HDMI / VGA board, but I'd love to finish the project too.
If there's anyone handy with PCB layout software, please let me know.

I'm not too bad with Eagle, but I couldn't turn out anything as good as Marshall can with Altium.
Here's a quick vid I did when the N64 was running via HDMI.
It also has an overclocked RCP from 60MHz to around 75MHz (CPU then at 112MHz), which might be a first for the console.

http://www.youtube.com/watch?v=NCbkDgCIKRQ
I just need a good PCB design for a proper HDMI chip, and it could be made to work for the Wii as well (soldering will be a bit of a nightmare without a custom flex cable).
OzOnE.