It appears that DIRECTV has a server of music where each of the tracks have been tagged with a bunch of categories. Then for each channel, the server randomly picks each track. With XM, the music programming is a lot better.
Unfortunately, it looks like U-POP is not being carried. I wonder if this is because U-POP is a WorldSpace Satellite channel. Also I wonder which 50 channels will be available for Total Choice subscribers. U-POP is is part of the Total Choice Plus and Total Choice Premier lineups.