First, if you are still using Gearbox, please make sure to set the Source on the left hand side of Gearbox to Instrument+Mic.  Once you do this, you should receive a message telling you that the Instrument signal will be sent via Record Sends 1-2, and the mic signal will be sent via Record Sends 3-4.

In Logic's audio tracks, you would need to set the input channels to 1-2 on one track to receive the Guitar input, and 3-4 on the other audio track to receive the mic input signal.

For further clarification, please go over the Gearbox Recording set-up guide on pages 2.7 and 2.34-35:

http://l6c.scdn.line6.net/data/l/0a060072153e747a739e447303/application/pdf/GearBox%203.5%20and%20later%20Recording%20Setup%20Guide%20(Rev%20A)%20-%20English.pdf

Regards,

Line6Hugo