I can’t hear the Difference in the change the low pass filter or the volume on my SVS subs

I only have one sub, SB-2000 Pro, and I keep the volume up as high as it will go, 0db.  I can clearly hear a difference on the low pass filter, especially between 40Hz to 60Hz.  I leave it around 50Hz and it fills in nicely.  You can adjust the filter in real-time with music playing.

How are you feeding it, line level inputs? 

Yes. Line level. 2 SVS SB3000s.

I settled on 60hz and 24 for volume, but as I said, I can adjust and don’t notice much difference, so it feels somewhat arbitrary that I have it set where it is.

Hey,

You need measurements badly.  The volume especially should be pretty obvious.