Having the factory ML system is decent, but really want to upgrade. Are there any known companies that make high quality replacement speakers and especially the sub in the package tray, as in kits packaged and designed to work in that model? It seems you could put a bigger, high quality sub back there. Or has anyone set up a nice system utilizing the sub in the package tray? It seems to me that a nice sub there would use the trunk as its box and you'd maybe make nice sound that way as opposed to building a box installed in the trunk. Looking for options before I pull the trigger.