PLEASE help with slim phatty / mopho as external instrument

[enthawizeguy]

Hey so i am trying to integrate my slim phatty and my mopho keys into live as external instruments. I am having trouble tho. I seem to be able to get the mopho working fine but i can't get the mopho to trigger the slim phatty. When i plug another midi controller in it works fine. I would like to be able to switch back and forth recording sounds from slim phatty controlled by mopho into live and mopho sounds into live. Also what is the best way to figure out hardware latency settings?

Thanks in advance,
Ian