Don't know about rolloff but our DSPeaker, Anti-Mode has a subsonic filter and basically, my understanding, it protects the subwoofer from going so low that it harms itself. You know how subwoofers are. Give them a few low frequencies to play with and a bit of unsupervised amplification and the next thing you know, they've gotten themselves in trouble.
When I do with and without measurements, the REW measurements taken with the filter turned on, after many reading, are the better for it readings.
Currently, I have the Anti-Mode provided, 25dB and 35dB boost in the on position as that gives what I consider to be the better graph in the <70Hz (one octave) of the graph. Understanding, when I post, in my opinion, graph reading and interpretation is a subjective "art" as once one gets their system "PROPERLY" dialed in, at eighty or ninety dB, in my opinion, outside the ideal of +/- 3dB, transient nuances of two to five dB, are going be undetectable as before one can notice any fractional of a second sonic dip, the sound track and visual before them have moved way beyond our ability to notice and recall.
The same goes for a dip or null that presents itself during a transient visually presented sound track. If a dip or null is a quarter to a half octave wide, one isn't going notice the sonic flaw. This is what my understanding is based upon reading but I've not measured and verified this point.
If a single frequency, of course you're going notice a ten of fifteen dB dip but if a visually transient scene with sound track is presented before you such as a comedy like "Liar, Liar" with Jim Carrey, I doubt anybody is going notice a momentary dip of a few ms.
The point of my above ramblings, have you measured the sonic output of your subwoofer system and if so, how close are you to ideal so you won't find need to overdrive your subwoofers?From what I've read on the SVS 16-46 CS-Plus,
they're spec'd at 300w, 4ohm load, 16Hz and folks have rave reviews on their output.