Erm, I think we're getting a tad mixed up but we're almost in harmony.

The DS card slot does not have 'access' to the GBA chips, apparently - and the DS itself is not powerful enough to run a GBA emulator.

As it stands, if you want to play GBA roms you'll need a slot 2 (the bigger one at the bottom of the DS) flashcard.

GBA Roms have to go on a flashcard that sits in the GBA card slot.

The DS-X, M3DS simply, R4DS can play DS roms easy peasy, but cannot run GBA roms themselves.