Rich,
I used the HSU for mixed HT/Music and IMO the servos are much better for music. I only heard the SVS in the HT demo, so I can't really say. HSU does make some sealed subs, I had the VTF-2, and ended up with one port plugged and one open. I have no issues with clarity, detail and dynamics with the servo subs but I'm using three in a distributed arrangement, so none of them work very hard. They don't have any trouble keeping up with either the Abbeys or the JBL's, both of which don't play real low but are quite high efficiency.