Wouldn't the harmonics be the responsibility of the main speakers? Especially if they are of higher frequencies, as harmonics usually are.
Another possible explanation for the SVS subs being less 'fast' or having less texture than HSU subs as originally stated in the post may be because the SVS subs do not have a low pass filter? I noticed from the frequency response charts from the SVS websites that the subs have a flat response, say 90 db from 20 Hz all the way to 500Hz when the chart ended, and still no sign of rolling off. All that midbass from the sub might interfere with the mains speakers, making it more difficult to integrate them well. I don't know about HSU subs, haven't seen a freq response chart of HSU subs.
One amazing subwoofer shootout i have come across is this:
http://ultimateavmag.com/features/604way/
I found it to be a truly educational read. Funny no one mentions the Revel B15 in these forums? Because of the price range?
