Guys, this is EXACTLY the dilemma I was in, when it came to choosing the 'ideal' subwoofer for my system.
It all boiled down to HOW much bass you want while watching movies. My VTF 2 MK3 is turned down almost to 1/3rd of it's capacity for it not to shake up the entire house, the window panes and the people around it. And mind you, it's not a small room. 300+ square feet is the size. It's power while watching movies might be surpassed by the 400w amp inside the SVS, but the question is, WHERE are you going to use the sub at insane levels like those?
Also, I was going to go in for bookshelves first, but people say it's very difficult to match a speaker with a subwoofer and have them perform in tandem. I am 10% close to getting that 'almost' perfect sounding amalgamation with my HSU subwoofer with my Dali Ikon 6 floorstanders, though I keep the subwoofer off most of the time while listening to music since the bass from the Dalis is enough, and SWEET. The sub adds a couple of DB to the midbass and the 'low' lows which is needed when I want to listen to some house music. But yes, the Dalis perform very well alone.
I have read on a lot of forums that HSU subs are musical. Expected a lot from this sub. And it has delivered very well. Haven't yet reached crazy SPL levels on this baby since the subwoofer is placed on a smooth polished floor and the spikes are not getting enough grip to dig into, which is causing the sub to SHIFT madly (almost like it's got wheels, LOL) at high volume levels.
Will be getting a carpet to place the subwoofer soon. I expect the performance to go up by a large margin once the spikes are dug into a thick carpet and the 'slapping' sound alongwith free movement of the subwoofer will go away.