If you get an 04 CC you will have room to mount the amp and Xbox. However if you get an 05 CC there is not enough room to properly mount an anything behind the rear seats (due to rear power window).
I don't have any experience with the Alpine Type-x speakers but I have owned some of there speakers and have been pleased with them. Plus, they will be happy with the 75 watts that you will be feeding to them.
I just bought and am in the process of installing Polk dBs and will let you know how they are. I am expecting them to sound nice in the truck. I paid $300 for two pair from Crutchfield.
Check out my thread for some pics of the 05 rear wall and you will see about the lack of room. Of course I am assuming that you don't have the truck yet hence the "planning stages".
My Installation.... in one week! I hope...