Thanks all - I did get in behind there and scoped out setting up a good sound system. Tons and tons of space...like, I can't believe they "wasted" that much space. They could easily have at least made a big drawer there above the fireplace.
Also, once I was in there, I saw this (photo)...
The original hole for running cables looked like someone had just punched their fist through...and then they did something that pulled the cables on a little run up and to the right
I know it likely doesn't make any difference...but seriously. Ever hear of a hole saw?
And also, there was that one sizeable 2-part wire just sitting there with no cap or anything on it. No idea what it's for...or if it was hot...but again, seriously? I taped the end up before putting everything back together
Have found a number of issues like that. Obviously I'm aware of the fact that my Silver Lake isn't exactly a top-of-the-line model...but there have been some fairly amazing instances of DGAF that kind of blow my mind.