First - I am not an expert - I am an enthusiast who like you is looking for a musical sub for a 2.1 system for ~$500 or less.
I have never actually listened to either on your list. But by reputation: Energy subs are OK but there are better for either music or HT unless you get a great deal; the SVS is an excellent contender and good value, especially if HT your major need.
Although not gospel, generally sealed subs are better for music only.
If you can afford it, the best choice would be a Rythmik F12 (that's what i have in my HT and choice it for excellence in music for SACD 5.1).
Assuming it's $650 (honey oak) or $700 (black) price is too much, then you are more in the market for my current search, a 2.1 musical sub for <$500. But save up for this and you will be really happy.
My short list:
- Emotiva Ultra10, $399 (soon to be released)
- Aperion Bravus 8D, $499
- Mosscade Titan 5.5, price not final
Good luck and have fun.