I disagree. If the coach is Sirus ready, it's Sirus ready, not that it requires additional equipment. That's how ours came, the OP's is the same vintage.
OP: The radio is mounted up against the firewall under the dash, and it's a PITA to get to! LIKELY, the DIN cable between the radio and the Sirius head has come unplugged. If you're not a contortionist to get under the dash and get your arms cut up with the slitwrap, climb up on the roof and look for the antenna. It will be on the front cap, or right behind it, on the left side. The antenna is ~2"x2", sitting on a metal plate sitting in a pool of sealant.Getting to the rear of the radio is easier, but when mine had this problem it was on the sat head.
As I said above, if you really want satellite radio, the Magnadyne is a lousy choice in general, and a lousy sat receiver..
Jeff - WA6EQU
'06 Itasca Meridian 34H, CAT C7/350