Iíve recently placed sub bass extension back in line with the FBQ2496. While setting up and I guess it has nothing to do with mains humming around 50Hz outputting mildly at soft volume level was heard it was heard much louder when the volume on the amp was turned up!
I used a simple means to stamp that electrical 50Hz Gremlin out! With a wire attached to negative on the RCA plug lead that goes straight to the active powered subs and by attaching the wire to the chassis of the FBQ2496 reduced it by 95% on one sub Eltax A12R and 100% on the Gale 30 12Ē sub.
This approach doesnít cost much and its not fully guaranteed to work it does take some trail and error so attach a wire to the chassis be it AVR or other and go around each phone RCA plug attaching to the negative until that humming or buzzing goes away!
As for the FBQ2496 itís a cool PEQ device if daisy chained looped together though A and B or from unit 1 A and B to unit 2 A and B you can double the bands from 40 to 80 bands PEQ and so on, but would get expensive and it will take up rack space as well.