Best and Loudest 6x9's

You are definitely on the right track... From my experience, Infinity CAN NOT BE BEAT.  Nobody else has the clarity.  Personally, I would do the Kappa 6x9's and a set of the Kappa 5.25" component systems.  Have a similar system in my vehicle, unfortunately MUCH more than the Kappas, but still same concept. (I had Kappas before and was happy, but the upgrade bug hit me again. :)

Infinity speakers can definitely be beaten into the ground by many companies. Image Dynamics, Focal, and MB Quart to name a few. Depending on how much you are looking to spend, I personally have had great experience with the Lanzar Vibe series 3-way 6x9's, as well as their 6.5" and 5.25". They are constructed in the way component speakers are, in that they do not have a hole through the middle of their cones, to hold the tweeter. I personally run high-end Focal Polykevlar 165K2 components, and would suggest them to anyone looking for the quality they provide. However, at the retail price of 653.00, these hand-made beauties are not easy on the pocket. I would suggest the Lanzars to anyone who is looking to upgrade to a speaker with a lot of power handling, clarity, and easily affordable.

I would suggest MB Quart DTE 169 http://www.mbquart.com/2003/en_US/products/prod_detail.asp?isArchive=&cat=auto&series=discus%20series&strt=1&model=DTE+169 they have excellent clarity and are pretty loud.

MB quarts are awesome, but they are pretty expensive. If money is no object then they're definitely what I would look at first.  Infinitys are really nice speakers and are a lot less expensive, and are probably my personal favorites for speakers.  just my two cents though

you can get those Quarts for around $100