I'd like to be able to record two guitars at the same time.  If I have the correct adapters for the two inputs, will the Mobile In allow me to arm and record on two tracks in GarageBand or any other DAW?  I realize that one of the inputs on the Mobile In is line level, but I could use the headphone output of my modeling amp on that channel. 

I'm using an iPhone 4, but would also like to know for the answer for the iPad.