I replaced my front 5x7's with JBL's which are a straight swap, they sound allot better than the standard speakers although the standard ones are not bad. If your bothered about bass then ditch the rear speakers all together i disconnected mine. Mid range and Top end sounds need to be directional, ie focused on the listener, bass is not directional you can run a sub anywhere. I had 2 12" 800W Pinoneer subs in the boot with an amp and the sound quality was out of this world but i got tired of the bass so swapped the subs for some vibe square 6x9 hidden under a custom made stealth shelf run by a 540w 4 channel amp which i have bridged. I miss the bass but it still sounds spot on specially when watching a DVD