Wanting to know if the 5.1 Surround sytem works only when DVDs are playing or whether it works with other stereo sources such as FM and XM. I have a 5.1 system in my Cadillac STS and it works with all stereo souces. It is great! I hope that the Enclave system is the same but I am not sure because it is only available with the rear Entertainment system. Can anyone answer this? Thanks much!