It's a frequency band off the satellite that always transmits all the channels, your reciever is picking up the signal and decoding the channel you want. Simple as that.

They have no concept of knowing your reciever or transmitting directly to it. It's just in their coverage area (Northern Hemisphere America's) you can pick up either XM or Sirius (both run different satellite constellations). The only item they transmit to the reciever is authentication for your reciever to play when you first subscribe - there is no transmitting from your reciever back to them...

BTW: Yes - I think I know what Omni is as I posted about a 1000 articles there over the last 10 years - but I choose to avoid it and stay on topic for what this is "FlyerTalk" - Just my 2 cents.