You should have underseat subs from the factory. Usually a pretty decent 3 way setup stock... At least imo, might be biased but my car sounds good enough stock with some EQ adjustments to bump the bass up (lower everything else) that it doesn't bother me. Maybe you're settings have been effed with. Aftermarket is always tits, but BMWs generally sound decent unless you have the most basic factory setup... I believe it's a mid EQ'd to hell and back... Very disappointing lol