Sorry for taking so long to respond. I don't monitor this forum very often. Yes, the Aux Ground is goes straight to the aux jack ground, common for both left and right. In practice, yes, I have to put a CD in the head unit and play it. Just like 686cody686, I do not know how it works, but none of the "playing" CD bleeds through the system. There is not additional noise either, no engine whine. It is a clean sound. There is no inability to make it loud as I want. Note though, I have only tested with an iPOD.