After research and many attempts at adding midbass I've come to the conclusion that adding internal woofers facing the wheel is the best way to go. The only downside is loss of bag space. At this point I'm willing to bend a little. I've researched a few different brands and I came across Bavsound Ghost. They make an extremely shallow loud midbass speaker that gets down to 40 htz. Has anyone used it? They are designed to fit under the seat of a BMW car.