Derick2k sent me a prototype of the audio merge kit and I installed it over the weekend. Install requires one to remove the two rca jacks off of the multi and install a pcb in their place. This pcb is powered via a 3 pin connector. You must tap 5v, ground, and the Dash signal from the multi...
I had a similar situation where my A-board suddenly stopped booting my multi. Worked fine with an original romboard but just would not boot the multi anymore.
The A-board I was first using with my multi just crapped out overnight a few months ago. Super frustrating. Wouldn't boot the multi at all but still worked ok with a street fighter 2 romboard...