Planning to order my SVS tomorrow (got paid at last, yeah). Thinking I will get the 20-39CS and the S700 amp, have the sub tuned to 17hz instead of 20. Still wavering between that and the 25-31.

Originally planned to get the powered version but it is not much extra to get the separate amp, and you gain quite a bit of flexibility. Mostly a much easier upgrade to two subs if you ever want it. You have a spare channel on the amp and you can buy the unpowered sub for a lot less money than if you had the powered version and wanted to upgrade to two.

Almost forgot -- my recommendation would be to look into SVS. It's $729 for the 25-31 and an amp, or $669 for the powered version of the same. If you can find a B-Stock, it will be cheaper (but they go fast).