Gonna follow your lead and install the Kenwood sub.Bumping my own bump...
The D pillar speakers were extremely easy to replace with a pair of Infinity Ref 3022CFX, and the rear doors with a pair of Infinity Ref 6522EX. I used a pair of PAC NSB710 adapters for the rear doors along with the Metra 72-5602 harness.
I also installed a Kenwood KSC-SW11 sub under the driver's seat using the PAC AOEM-MAZ2 interface. That made a BIG difference! I'm able to turn the bass down a little on the Bose system, and instead drive it through the more capable (clearer, less muddy) Kenwood sub. A little futzing around with the gain and low pass filter and I'm really liking this change.
I left the front doors alone as much as it pains me. They only get bass frequencies, and installing the Infinity Ref 6522EX would have been a waste. Possible future upgrade with the Earthquake Sound i82SWS or Infinity REF-FLEX8, but I feel like I'm at the point of diminishing returns.
Total investment was $440 plus a few tools, and it was worth every cent. Is the PAC AOEM-MAZ2 required or just a plus. I would think the sub comes with it's own. Don't know much about this stuff... learning.