I'm not sure that question has been brought up before; I do know that the portable XM units have some functionality that is not on installed XM systems. If you figure out or get an answer; let us know. I am not aware of any kind of rewind feature for the installed XM systems in our Lambda's.
I have a friend with an aftermarket Sirius radio in his truck that will do that. I do not believe any factory GM XM radio has that feature, but I would sure use it and like it if it were available. The other thing that would be handy would be "on demand" programming like cable TV has. I solve that shortcoming by using audio books and iPod.
At some point, though, one still has to pay at least a little attention to driving. :thumb:
C Traz - You're right, that's where I saw the feature. I had forgotten.
My wife and I test drove the LaCrosse and saw an Enclave and got interested in that and ultimately bought a Traverse from the same dealer who sells Buick, Chevy, GMC, and Cadillac. (They used to sell Pontiac, too, at the same dealership.)