Just a quick note on XM and Sirius. We have both. XM in my car, and Sirius in our new minivan (came with it for 1 year).
Sound quality is about the same. Highly compressed. Not like MP3 compressed that still sounds pretty good for a digital recording, but noticably compressed. In our van, I only have bass/treble controls, and it always sounds "muddy and muffled". In my car, I have an aftermarket (nice) head unit ("radio") that I can control a LOT of the audio, way beyond just a graphic equilizer, and it sounds pretty good.
Still can tell it is compressed satelite radio, but not nearly as bad as the van.
The home kits are nice in that you just plug in the "tuner" and go. Some power, if not all, will be proprietary to some degree. Others may work on a universal power adapter where you have different connection options and can select voltage, etc.
I am not sure about hooking up satelite radio to a receiver at home. If you can really tweak the sound it will be OK, but still nothing great. I do know that Dolby or someone is working on new algorythms to help "expand" the compressed audio so that it doesn't sound so bad, but that is probably a year or so away before we will see that.
As for the real differences in the service providers, it is really just stations. I would say that Sirius has more "hard core" stations like Howard Stern, etc.
Be sure to look at satelite receivers with the options that you want. For example, my XM receiver has a 30 minute "memory" so I can go back 30 minutes of what I was listening to. The Sirius that is built in to our minivan does not have this feature. Also, the XM one I have shows a lot more information like station, song title, artist, etc. The built in one for Sirius only shows station.
Again, this is not a Sirius or XM thing, but a receiver options thing.
