Which games? DM and DML has been merged into one project with one developer, so other than where it looks for to get the game data, both should work the same.
But to answer your question:
Only one Mios can exist on a system. Installing one will overwrite the previous one.
But more than likely, if you are have DM working with a few games and others aren't working, they likely won't work with DML, either. They are likely bad rips that needs to be redumped. So let us know which games you are having problems with, and if they are games I have, I will let you know that it works fine with DM.