I don't have a Line 6 Pod XT but looking at the specs and the Line6 website it looks like you can output the signal to Logic. Their website suggests the Line 6 will act as an audio interface.
There are two ways I would go about doing this.
1. Use the USB cable from the Line 6 into your Mac.
Install the Line 6 software:
Go to Preferences > Audio
Select the 'Devices' tab and Under Core Audio's Devices select the Line 6 Pod.
Click on 'Apply changes' at the bottom of the window, record enable an audio track with Input 1-2 selected and you should be able to hear the input from the Line 6.
2. If you already have an audio interface:
Set up you interface as normal.
use two line-out leads to feed the stereo outs from the Line 6 into your audio interface's Input 1 and 2.
In Logic, select an audio track and select Input 1-2. Now record enable and you should be able to hear sound passing from your guitar through the line6 into Logic.
If you can hear your guitar dry but not the Line6 amp effects make sure that 'software monitoring' is turned on in the Preferences > Audio > Core Audio window.