I subscribe to neither so those that do can speculate on what it means before the official announcement on Tuesday.
http://www.nytimes.com/2007/02/20/business/20radios.html?_r=1&ref=business&oref=slogin
Likely you will continue to get your XM or Sirius stream as always on your receiver, no matter what the service provider is called.
You will likely be able to get the stuff that's on the other channel (eg the sports you want) but that will probably be a premium, extra-cost service. Also uncertain is what happens to people who bought a lifetime subscription - does that cover only as long as the service has the same name, or its successor, and if so, how much of the service.
They said a decade ago they'd never merge and now they're saying they didn't expect things like iPod and sooner or later streaming WiFi / cellular data music / VCast / WiMax to the car to be competitors. Which they are, sort of, so long as you're in an urban area. Not a lot of VCast streams transiting the Great Plains.