Most music on the radio, and even a bit on satellite lose those frequencies. Fading to the rear won;t do anything to increase the output, it's not like and old 4-channel system from back in the day. The sub has it's own channel and the sub control is all that controls it seperately from the main volume.
Mine thumps pretty good, especially for a factory sub. In most cars you never know it's there. I used to work in car stereo when I was younger, and still have some ghetto subs in my mustang, that never get turned up anymore lol, so I think I'm a decent reference on the subject. If you're not hearing it at all, run by the dealer and have them check it out.
EX-L w/navigation, Polished Metal Metallic w/Ivory interior