Mbox 3g: Midi input for guitar?

I just bought an Mbox 3G. I'd like to record 2 guitars and one mic simultaneously. The ads said it was a 4x4 simultaneous audio device with 2 xlr inputs and 2 1/4" inputs. What I thought I would do is run the 2 guitars into the 1/4" inputs and the mic into one of the XLR inputs. Of course when I opened the box and looked closer, I realized that you couldn't use all 4 of those inputs at the same time, you had to select either the one on the front or the one on the back. I'm hoping this is only a minor set back.



My guitar pre-amp/effects processor has a midi in and out as well as a spdif out. I've never used these outputs before, so please forgive my ignorance. I bought a midi cable and ran it from the output on my pre-amp to the midi input on the mbox. When I bring up pro tools express and attempt to assign this as one of the inputs to an audio track, the only options I'm seeing are "In 1" and "In 2" from the mbox (along with a bunch of bus tracks, which I'm unsure what to do with). How do I assign the midi as an input to a track?



Thanks!