You use the BBM or the BBMO to import the .drm file. If using the BBM, don’t forget to activate the kit by clicking on the Drum Sets tab, scrolling to the bottom of the list and checking the box.
As long as you map the drums to fit what’s available in the kit, they should work. Same goes for the bass, keys and other instruments. For example, Phil_Flood’s kits usually include a file that tells you the octaves that the bass and other musical instruments are mapped to.