Subwoofer for Beginner

Dhcod, you have a very nice system. Buy a sub which is built for music, not home theater. I went with a cheap model a few years ago just to see what a sub could do for my system and the end result was that all the detail in the bass was lost, the sound was no longer musical.
I think you need to be in the $600+ range like the SB-12NSD or a used REL or Velodyne.

Rythmik subs available through Ascend Acoustics provide phenomenal bang for the buck.

There was an Audio Asylum member and speaker builder who built a subwoofer using a Home Depot plastic bucket (NO kidding!) and a Parts Express driver. According to all who heard it, it was pretty darn good. The build was easy to do and the cost was very nominal, less than $100. I think this is a the way I'd go if I were you.

Here is the link:
http://thehornshoppeforum.com/index.php?topic=406.0

-RW-

HSU Research specializes in subs and has good return policies/user support. The VTF-1 Mk2 is very musical, well reviewed and on special direct from site for $419.

http://www.musicdirect.com/p-77339-rel-t-zero-subwoofer.aspx
It's REL, small footprint, free shipping.
Will give you more than a taste of a musical sub I guess.