thanks folks, ill give the plywood a try.

How about the difference between max output and max extension? Is there any reason to leave it in max extension mode, or does it generally do better in max output? If I go with max output, how much will I miss not being able to play the frequencies below 25Hz?

And also, what is the volume range that this sub safely can handle. As I said previously, I used to run it on about 3, but just moved it to 4..but, how high can it safely go without harming the sub?

You mentioned to place the sub right behind the couch. Does this mean right behind the couch in the middle, or in the corner, and, would it be best to place it behind the couch even if it's not the optimal position as discovered by doing the sub crawl?