I'm thinking on implementing something similar to my other frontend, EmuCon. Select two cartridges in the games list and hit ENTER (or mouse double-click).
Then a slots dialog would presented so you can choose what ROM goes into slot1 and what goes into slot2. See attached picture. -slot1 and -slot2 parameters are OK for this situation, isn't it ?
But, a7800 and odyssey2 machines has only one cart slot listed in -listxml output. Does MAME accept -cart2 as parameter for these machines anyway ? I'll have to download the voice ROM and a game ROM for Odyssey 2 so I can test this.