This is the first time I've had XM radio and it might be my favorite feature right now. There are so many great channels to choose from. I even listened to one of the comedy channels yesterday and I was cracking up as I was driving. (I probably looked like a crazy person now that I think about it.)
The 5.1 system is unbelievable. Now, I couldn't comment on how quiet the car is 'cause so far I've had the radio cranked up and the sunroof open. I love this car!
The link says you need new equipment and it's just now rolling out so I highly doubt the current radio could handle it.
However, it also says that HD channels can also be played on current XM radios so perhaps it'll sound a lot better even if it isn't able to pick up the full HD affect.