I am looking to improve the stock HU. I do not want to lose my steering wheel controls or fuss with rigging up an after market HU to work with it.
So can I add a after market EQ or sound processor to the stock HU? Will it improve the stock HU sound? I need the advice of the all knowledgable audio guru's on here to set me straight.

To give you an idea this is what I had in mind: Pioneer DEQ-7600 Car Signal Processor

^ Listen to BIGRIG. An eq would be a bitch to integrate with the factory system and would also be a band-aid solution to the problem. The real problem is the speakers in the E are weak. Cure the disease; don't treat the symptom.

First of all thanks for the replies. When you put it that way it makes sense.
Guess my better option is to find a good installer that can do a solid job of hooking up a HU to the steering wheel controls and swapping out the speakers. I got about $800 MAX to work with but would like to stay around 600.

I think you're in a bit of a jam with your budget and what you want to accomplish. I really like the EX head unit especially since you have XM built in and also the aux jack and the ability to get the ipod link from Honda. It's full featured and it's stock, hence looks stock and that deters theft. I've seen 2 products on the market that you should look into for future upgrades. http://mobile.jlaudio.com/products_cleansweep_pages.php?page_id=94
JL Audio: Products
http://www.alpine-usa.com/en/products/series.php?category=P-FIT
Alpine Electronics of America, Inc.
These devices clean up the signal and equalize it for use with after makerket amplifiers. But you do need to use amplifiers with these. There are cheaper black boxes available but they do not perforn the DSP and equalization that these units offer.