So I have the Alesis Multimix 4 USB Mixer. I use Logic Express 9. I can't figure out how to do multitrack recording. I plug my yamaha keyboard into Line 2 and my mic into Mic 1. How do I "assign," you could say, each mic to it's own track? I want to be able to edit the piano and vocals separately so I can use different effects with each track. Does that make sense? How do I go about doing this?