I'm in the same boat as Sushi, and cannot give you a face to face comparison. Unlike Sushi, I have the SVS you are looking at. I really like it, but my guess is that they both sound great. The concern that you might want to watch out for is size - the SVS takes up space. It stands about as tall as my M80's.
If you haven't gone there, I would recommend going to ecoustics.com - they have reviews on a whole lot of subs, and a few months ago actually did a comparison between SVS, Hsu, and I think Axiom. (although I don't think it was these particular models)
One other similarity I have with Sushi is using the sub for all listening. I am at least 90% music - and wouldn't even think of listening to my M80's without the sub. Without dominating, it just adds a whole new dimension to the music experience.
Good luck with the sub. I cannot see how you can go wrong with either choice.
