I've heard the SVS PB12 and the ultras, they are nice subwoofers. The company is probably the only Internet-based speaker company I actually take seriously. There may be another, but I can't think of it right now. So, if your looking to buy a subwoofer over the Internet, I think that's your option period.
Velodyne makes nice stuff, I think you'd be happy with it also. Different sounding. I haven't heard the 5000R though, so I can't compare the SVS to it for you.