I've had this Yukon for a little over a year and a half. I don't know much about stereos. Aftermarket stereo was installed by previous owner. Probably doesn't sound any different than the stock one. Right front speaker did not work. It had the speaker with a tweeter. I replaced with the same. Sounds OK. It has a aftermarket subwoofer in the left rear where a stock one was. I don't think it was a Bose setup from the factory. They cut the wires at the amp and bypassed it (first pic). And/or ran wires to the speakers. (second pic-has one in both front doors) What is this? And what does it do? I cleaned it up before putting it back in the door. I usually don't drive it that much but when I do I would like to have the stereo sound good. Should I just rip everything out and start over? Or can I make it sound better?