On my 2012 XT, it us under the soffit of the cabinet that holds the radio. If you sit in the couch under it, and look up at the bottom of the cabinet, you should see it.
Right on the face of the stereo unit. Upper left corner above the display to the right of the on/off switch. Mine is a Jensen unit that came with the trailer in 2009. Yours may be different.
UPDATE-After removing the radio/dvd unit from the cabinet I found that only the front left and right rear speakers wires were used from the factory. I changed the wiring to use the front left and front right wires. Than I added 2 speaker ON/OFF switches, one near each outside speaker under the cabinets.
Thanks for all the replies. GARY