This is the unit I installed.
Here is a link with specs...
http://www.circuitcity.com/ssm/Custo...etailReview.do
Without this getting in to a useless Flame war about XM vs. Sirius, let em give you my perspective having owned both.
Remember, you may prefer XM. It does have things that appeal to a different crowd. To be fair to XM, I did like a couple of things. Baseball is only on XM and if you travel and are a Baseball fan, XM is a must. The have a cool channel called "Cinemagic" that was cool (listening to the score from "300" or "The Black Hole" was cool)
Here is what I did not like. XM tries to smash too much stuff on to one channel. For example, their "FRED" station tries to be a progressive station, but you get music from the last 30 years in no particular style other than "not pop". They also play the most obscure tracks in the world. The direct comparison to this station is "First Wave" on Sirius. This channel is progressive music from the 80's and focuses on the music that was influential in the movement and was actually played on college radio stations.
XM's biggest problem with the stations that I listened to was the absolute crap selections of whatever artist they choose. The artists were good choices, but the songs selected were b-sides and strange concert recordings.
Don't get me wrong, there are some artists that I can not get enough of and love the obscure stuff....but most of the time you just want to listen to the good stuff and move on to the good stuff from the next artist.
Another problem that I had was that the actual stations missed the mark for me. On Sirius, some of my favorites are the "classic vinyl", "Punk", "First Wave", "Classic Rewind", "The Spectrum", and "Margaritaville"
I am not a Howard Stern fan, so I don't listen to that.