Welcome to the forum, schmaughan!
First, did you try to customize the keymap within BFD2 when using the DM10? I think there is the problem.
Some weeks ago i'd posted a link to an entry in the FXpansion forum with a DM10 keymap for BFD2, but it seems that this entry isn't available anymore.
So try the attached .bfd2map file. It's for the Pro kit and you may have to tweak it a bit when your are on the Studio kit to map the fourth pad.
Good luck!