Yes, some of their channels are broadcast in 5.1. I pick some up once in a while on Cinemax and Showtime I think. They also have (I think 10) PPV channels that are always broadcast DD.
Most of the PPV channels. HD-HBO, HD-Showtime, HD-PPV, Showtime East and West, Starz East. There was a press release around December of last year that stated all of the channels in the Showtime unlimited package would be upgraded to DD. Unknown when.