Insulation cuts heat loss but does little for blocking sound. You should check local code and pracice for insulation in the walls. If you want to cut down sound, then you should look at doing the ceiling with a double layer of drywall with Green Glue in between the layers. You might also want to use resilient sound isolation clips and things like rubber joint isolators and soundproofing caulk. Also, keep the cuts into the ceiling to a minimum (like eliminating recessed lighting). The ceiling is the most important, but flanking sound up the walls can also be a problem. Really depends on who quiet you want it. The are good articles on these topics on the Green Glue website and on the website for the SoundProofing Company (no affliation with either). These techniques can really makes a difference.
Wall Insulation
I am building a home theater in my basement. How important is it that I insulate the walls? I will for sure insulate the ceiling but what about the walls. The basement is very dry warm in the winter and cool in the summer.