I have a LX and swapped out the factory speakers for Infinity Kappa 60.11cs components in the front doors and Infinity Kappa 60.11i co-axials in the back doors. They sound great.
I want to ad an 8" sub, but I need to do more research to find out if there is a low level output on the backside of the head unit to access instead of tapping into a high level from another speaker.
I really like the Harmon Kardon in my EX. If anything I would consider adding more sound deadening, and quiet the interior even more! No need really to swap stereo components yet!