That's just it. When XM first came out, the signal wasn't nearly as compressed as it is now. Because they've stretched really, over 200 channels into XM, there's no dynamic contrast, and there's no 'depth' to the sound, for those of us who are musicians or audiophiles. Basically, there is no loud, and there is no soft. Everything is the same volume, due to the compression of the signal. Take a listen to a song called "Sugar We're Going Down" by Fall Out Boy. Horrible song, but listen to the quality of the music that you are hearing. It is such a loud song, that it almost comes across as 'digitally distorted' for lack of a better phrase.
Now, try and listen to the same song again, on XM 21, or 22, and you'll instantly hear the difference in quality compared with the ClearChannel run stations versus the XM ones. ClearChannel gets a certain amount of bandwidth, and they've only got 5-6 stations on it right now, 3 of which are talk, and three are music. You'll notice what i'm talking about it.
It really is quite a bummer, because I don't think there's any plan to fix this, or make the audio quality any better. I have XM because I'm on a family plan, and I'm from Cincinnati, so I actually enjoy XM 173, 700 WLW.... I have no idea what SIRIUS sounds like, but on my DISH network TV receivers, I can still hear the lack of dynamic contrast, and the overall 'compression' of the sound quality.
I'm interested to hear what other people think about this as well.