Here is some info from the X3 Advanced Guide:
MIDI Ch (POD X3 Live & POD X3 Pro only) – choose from MIDI Channel 1-16, or select Omni to have POD X3 Live & Pro respond to all MIDI channels, while transmitting on Channel 1. The MIDI channel chosen from the display user interface will be used as the Channel for Tone 1. Tone 2 will use the next MIDI Channel.
When program change messages 0-127 are received, POD X3 Live & Pro will recall User Presets 01A-32D, and will transmit those same program changes as presets are selected from the POD X3 Live & Pro hardware. It also echoes all program change messages it receives, so it can be connected “thru” to another MIDI device.