Ok I had one very nasty experience in my last house where my home theater lived in my basement. After living in my houme for about 6 years I knew when it rained hard for several days there would be a leak spring up in the far corner of the house. It wasn't in the HT area, but directly behind it in the storage area. I was able to channel it harmlessly into a drain, so I didn't bother doing what the contracter said would have to be done, digging up the front yard down to the bottom of the basement wall to fix it from the outside. They said that was the only way to truely fix a leak, as patching it from the inside would only hold temporarily until the water found a different path to get inside. So for 6 years everything was hunky dory.
Then during a particually heavy storm our city sewer system became overloaded, and sewage flooded up through the floor drain and into the interior of my basement a foot deep. Our next door neighbor lady had lived in her house for 35 years, and she said that was the first time that had ever happened in that area. But it was enough to make me realize that you never know exactly what might happen. I was very angry when I found out that our 'full coverage' homeowners insurance did not include flood insurance... "but how can you call it 'FULL COVERAGE' if it doesn't cover everything"??? I protested. Guess that's why you have to read the fine print.
So anyway I tore out all the carpet in the basement, threw away the couch, coffee table and the Sony floor standing speakers I had at the time (no big loss) and started from scratch. I build a stage a foot and a half off of the floor that extended out about 3 feet from the false wall. That was where I put my new 65 inch rear projection TV, and my new Cerwin Vega towers speakers. But I too had very low ceilings in my basement, so I couldn't afford to put a subfloor throughout the entire bsement either. So under the rest of the HT area I laid this flooring that was only about a half inch thick. It looked like tile sort of, but the bottom was made up of several round nubs spaced out from eachother so that when you laid it down it would allow water to travel underneath them into a drain without soaking whatever flooring you put down (unless the water rose past a half inch). On top of that we had a pad and carpet laid and it was all very solid, felt as if it were sitting right on the concrete, but it had that water barrier built into it, and didn't take much of the ceiling height away at all.
The stage was just in case we had another major flood so the electronics wouldn't be in harms way. But that set-up worked just fine until I moved in with my fiancee here last year. Might be worth looking into if you have any moisture issues at all.
