Interesting. I know of a few of these combo boards in Black Knights running fine.
If memory serves me right, version 3 boards (MPU327-3) onwards have switch matrix problems with Black Knight where the game doesn't register and kick out the second ball in play. Not sure what version the sound issues started, could have been version 3 or version 2, don't quote me on it.
From another forum:
"Please note as of 1/5/2018 System 7 games (including Black Knight) are no longer supported, Rottendog is only supporting games System 3 through System 6. A parts change due to availability created a problem making it unusable in most System 7 games, it supposedly works in some, and Rottendog cannot find a solution."
