My 2006 has NAV, so no way I will change the radio, but I was wondering if swapping out the rear 6x9's with something with more range (maybe Alpine) would help in any way?

I may even do a sound-proof on my Accord. I did it on my Tundra and let me tell you, it was quieter than my Accord, and the Stereo really cranked.

Here is how I did my Tundra (which I sold back in Feb so the wife could get her Pilot). I have a ton of the BrownBread left. Just look at "Silence of the Tundra". It was a fun project.

http://gwfweb.com/tundra/