Picked up a 2015 Merc GLK 350 last year. The most basic model, so stereo system seems less than stellar. A bit muddy and sound feels like it's coming from below you. Al & Eds (local car modders with good reviews) took a look and only recommend a subwoofer (in narrow space underneath passenger seat!) and bass adjust knob on dash for $500. Could help free up main door drivers from low end, but not sure it's worth it?