SVS vs. Velodyne?

I'm new to the moderate to higher end HT scene. I bought a HT in a box for my Mits DLP and it failed miserably.I was at Tweeter looking at some upgrades and was impressed with the Velodyne DLS3750 and he SPL1000(although I don't know if either will be large enough for my application, my living room is 12x24). A friend of mine then told me about SVS subs. He never heard one personally, but he sells a fair amount of equipment on this site and told me how everybody here raves about them. This sub will more than likely be coupled with a set of Polk RTI series speakers and all hooked into a Denon 2805 or 3805 receiver. I suspect with this upgrade I will be blissfully enjoying an equal amount of music and movies. I'm not looking to spend buckets of money yet (no more than $600 for a sub). Any constructive input for the FNG would be greatly appreciated.