It sounds like you have room node issues and/or your sub placement needs work. Another problem is that the SVS subs are known to have a mid-bass frequency hump which can be accentuated by your room. I would use the crawl method to find a better place for your sub. Usually one third of a wall-length across the frontwall or sidewall gives better response but less room gain. The SVS subs are known to have unlinear response below 24hz which need equalization as well. You may need to think about basstraps or an equalizer if you can't find the right placement. I uses an SMS equalizer to get rid of room nodes at the sweet spot and strive for flat FR for the best sound quality. Or do what I did and buy the EP Axiom subs that way you don't need to worry about lumpy response from the subs.
