As some of the folks above mentioned, it won't be necessary to have your sub from the same manufacturer as your speakers.
While some folks haven't been overly thrilled w/some of Athena's sub offerings, I'm using a AS-P4000 in my secondary setup and it does a pretty decent job with movies and music. It's not much to look at, but for a small sized room (less than 1,800 cubic feet), it does a solid job when not overdriven and within reasonable means. I was able to pick one up for less than $200 shipped and in this price range, I don't think you're going to find much better. I have an SVS 20-39 PCi in my main setup, so I know what tight, deep bass should sound like and the P4000 isn't a bad option for the money.
Also noted above, if you can provide your room dimensions, budget and intended use (movies to music ratio, e.g. 50/50, 70/30, etc.) we may be able to suggest some options for you.... -TD