DualFilter is the only surround resonant filter I found, and it sounds ok BUT it does some filtering even with all the settings to their neutral position, making it not too useful.
The best feature that it could have is to be 100% neutral, but if it’s not possible, please add a mix knob or, even better, make a “pro” version with true neutral position and saturation 
Regards.
PD: BTW, anydoy knows ANY surround resonant filter with neutral position?