Do they use a CD? Or some other source? And how do they get such a diversity of genres and selections?

I have to say, on the channels I listen to(High Standards, Real Jazz, Watercolors, Cinemagic), the overall presentation is impressive. I mean, the vocals sound very good, bass instruments are also very defined. I understand that due to compression, the highs are suspect.

But just from the overall presentation, I suspect their source is very good.

There is some info at places like www.xm411.com and xmfan.com but from what I have seen it is mostly CD's. They have a huge archive room where they have to keep the physical CDs of every song they play and the RIAA stays on their back about it through audits. They have all the CDs ripped to a huge music library/server system that goes to teh control rooms.

XM's main music library is a huge storage area network (SAN). Originally, it was based on IBM SAN components, but they have moved on to Isilon IQ storage cluster arrays. They used to quote the size of their IBM system as 22 TB, but I'm sure it is much larger than that, nowadays.

Loudeye was originally contracted to rip CD music content into the SAN, where it stored as MGEG-2 at 384 kb/s. Playout is through a Dalet digital playback system. The individual studios have CD players, so that live-air talent can playback CD content locally.

They probably have one the best music libraries on earth!