One issue that you may have never considered until sinking thousands of dollars into a home theater system is room acoustics. All rooms are not created acoustically equal. Hard reflective surfaces will bounce sound around and make it seem louder and tinnier. Soft absorptive surfaces like carpet and cloth muffle and reduce sound quality. Getting precisely the right mix can be a daunting project, and if you have already laid out a tidy sum on furniture, electronics, and decorating materials, before you go any farther you may want to consult a professional.
You will also want to address the issue of how much noise gets in from outside your home theater room, as well as how much noise you want to get out. As a general rule, you want about 50% of the total room surface area – wall, ceiling, and floor area, absorptive. Most of these absorptive surfaces should be within the front part of your room, with the harder, reflective surfaces toward the back.