Are you on the latest version of HEN? Is webman / webman mod installed and running? If so, that's probably why you're having the black screen problems with multiman. Only time I've broken a game from DLC was with just HAN trying to install the DLC for Ds2 (digital version) lmao. It only corrupted the game and I had to reinstall it.
I'm on HEN 2.0.0 with just multiman installed and the only time I've had black screen is when trying to launch incompatible backups, only time I've had worrying freezes was when messing around with retroarch lmao. Other than that, I think it works just about perfectly for my needs.