Umm this is really being made a bit more difficult than it has to be. Get the latest available version of MAME that you can and dump the roms into the roms directory. The ones that MAMEx can read will be listed and the ones that aren't listed MIGHT be listed in a future update of MAMEx. If that ever happens......
From the MAMEoX website....
"Posted By: eabair
Date: 2003-05-16 13:14
Summary: MAME core 0.68 released
Just noticed that a new MAME core version (0.68) has been released, and I'm now updating MAMEoX.
Expect a new release (0.64b) including the latest MAME core by Monday or Tuesday at the latest."
Course I still think they may have compatibility but have lots of issues with the emu's core.