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.

I think it's more a matter of VERY attentive listening, and after really learning what you are listening for. I run one SB-3000 and two SB-2000 subs and subtle setting differences can also be very subtle to discern by ear as well, especially when buried under other music, usually louder.

I'll sometimes run just the SB-3000 and go between pre-sets to A-B the differences and learn a bit more while critically listening (which is not too often these days...  :-)

I use measurements and feel they are very important in getting the best clean match and overall sound. A DSPeaker Anti-Mode 2.0 tames the room and speaker bass and the subs are dialed in later for a flat, measured in-room response.