I had a Sony CDX-GT4301P radio installed in my truck at Circuit City tody. This is a Sat ready unit so I added XM to the radio by purchasing a CNP2000uc unit and having it installed. I set up the radio with XM and XM works. However, there are no instructions as how to change XM channels or how to scroll up or down. No one at Circuit City knows nor is there any info on line from Sony or Audiovox?? Can someone assist me with this?