Serial Ports (Main Processor)
Serial: Secondary connection to CoProcessor
Serial1: Primary connection to CoProcessor
Serial6: FTDI Connector (underneath XBee)
Packets send to Serial1 (CoProcessor) will automatically be forwarded to the XBee. So if you wish to use XBee, use Serial1.
Serial Ports (Co Processor)
Serial: Secondary connection to MainProcessor
Serial1: XBee Connection
Serial2: Aux Port - pin 4-5 (respectively tx/rx) on J1
Serial3: USB Port
Serial4: Primary connection to MainProcessor
Packets incoming on the XBee will automatically be forwarded to the main processor which will receive it on Serial1.