Hello,
I found that adding a sub & an amp to power the sub and the existing speakers made a huge difference, without the need to replace any of the AR speakers. Once the bass is not going to the woofers they cope quite well.
Amp was a modest blaupunkt 4 channel with 2 powering all the speakers, and the other two bridged to supply the sub. The sub was an 8 inch alpine D type, which can run in free air. I made a simple MDF enclosure in the corner of the boot, behind the wheel box.
Kevin