Garageband - 2 keyboards 2 instruments?

Okay, I have an M-Audio Keystudio 25 and a Casio WK-200 both work great with garageband and I have Midi to USB hookups. they both work great! now, i am performing live, and I wanted to know if I could ign one keyboard to a certain instrument and the other keyboard to another. i already have multitrack recording on, i just need to be able to play both tracks with the two keyboards. Thanks!