Garage Cabinets, Garage Storage, and Garage Organization

I just bought a 2000 E320 and am not satisfied with the Bose sound.  There's no bass and the sound is flat.  I've gotten different opinions on what to do.  I thought maybe a subwoofer would help, then someone advised a new head unit, and then someone else said it's my imagination.  Any advice from those of you who know?  And I'm not prepared to invest big bucks in a new sound system.

From the discussions about modifying the original head unit of the audio system just to enable their MP3/Ipod player to play on the audio system which requires additonal gadgets/devices/adapters that cost more than $500 for the adapters, etc, etc... and the labor. I also wanted to connect my Archos 605 wifi with 160GB of MP3's but instead of going into this route, I'll just buy a new car stereo receiver, maybe a JVC or Dual with features like HD radio tuner and Bluetooth and 2-speakers(stereo only) and a sub-woofer. These units will be installed somewhere under the the dashboard. It will be powered by just plugging the unit to the cigarette lighter outlet. I'm still looking for speakers & subwoofers similar to the Bose cubes, small enough, to be installed underneath or under the seats or anywhere hidden with enough power to really rocks me.
The cost is less than $500 and it will not change the original stereo system. It can be removed anytime. Any recommendations or comments.