Pooht
I know I'm a bit late into the discussion but I'd love to comment. First of all, putting 4x6 plates AND speakers in your kick panels will do nothing for your stereo except make it loud by 1-2dB and decrease your image/soundstage quality. If you're unfamiliar with what that is, it's the stereo's ability to reproduce the instruments accurately, so that you can tell where the vocalist was, and where the guitarist was.
Also, my suggestion would be to drop getting rear speakers altogether with. Not only will this also degrade your imaging, you might add 2-3dB, but at a higher cost, and lower sound quality. Sure you could install an expensive DSP to put a time alignment delay on the rear speakers, but your chances of getting it set up properly, are slim to none if you don't have experience doing so.
Go with one nice set of components up front in the Q-forms, they sound great for pre-built pods

If you have custom pods fabricated, they'll cost in excess of $800, and anywhere up to $1500 depending on how good the shop it as working with fiberglass (or another suitable material). Compared to $200 a set for the Q-forms, they're worth it.
Brands of component sets to look into are the Boston Acoustics ProSeries 6.5's, Dynaudio, Focal, Diamond Audio, MB Quart, and certainly the Kappa's will sound pretty good but the other brands I mentioned will beat them out in most cases as far as accuracy is concerned.
Some people have been mentioning the HCCA subs from Orion, while these are very very loud, they aren't the most accurate subwoofer out there. Sure if you love bass, they're great, but if you want something accurate, JL Audio W3's are good, Alpine makes a nice sub in the SWR series.
Going back to the whole 10 vs. 12 deal, 10's are nice, very punchy, and musical. Don't get me wrong, but a good 12 can be just as musical as any 10, AND have a bit more low extension. Don't sell yourself short, get yourself a 12. IMHO, a 12 inch driver's ability to reproduce low notes is just a bit easier, and for that reason, makes it sound just a little bit sweeter.
I took a listen to the Infinity Perfect subs not too long ago, and they're also very very good. Highly recommended there, but I don't give quite as high a recommendation to the Kappa's. They're good, but there are better components out there.
If I can help you any further, please let me know. Hope this has helped so far.
dm