In my last house I built a large basement room solely for the purpose of audio listening. Some of the items that I could suggest would focus on the infrastructure - primarily electrical circuits and cable systems.
Ensure that you have an adequate supply of circuits installed. My suggestions are to have dedicated circuits/breakers for the AV equipment, lighting, and accessory items within the room. While this may have no effect on AV quality, it will ensure that you do not have a breaker trip, and you have to fumble around the room! I would suggest 2 circuits for the AV equiment, 1-2 for accessory outlets, and one for the lighting. This assumes your panel has sufficient capacity. If you are pulling wires from the electrical panel, a couple of more add little cost. Also make sure your grounding is sufficient to each box.
Also, you indicate that you will be drywalling. I did the same, and placed conduits inside the walls to allow future expansion I simply terminated them in wall boxes with matching covers. This allowed me to pull any new cabling into areas. This came in handy when I wanted to add surround and network connections. Even if you put conduits to areas, and sealed the ends, at least your flexibility is ensured. This of course is a personal decision.
We could address the issues of materials, which could address acoustical concerns, but you indicate a need to be practical and functional, without sacrificing decor. Based on some of the rooms I have seen - and the thread that once existed - I would agree with you on that point.
If I remember other items, I will be sure to post.
