I usually don’t use EQ solely for equalizing the low frequency band from sub, because that is too wasteful. Rather, I use it to equalize my three front full range LCR channels. As you can see from the back, there is a XLR and 1/4 inch input for each channel and you can use either one of them for connection, but you can’t use both of them. The output is internally paralleled so you can have total 4 outputs from 2 inputs if XLR and 1/4-inch jack are used at the same time. The XLR subwoofer out jack is a simple mono sum from the input signal and you can use it for another subwoofer. You put EQ behind your 950 (Pre-amp out to EQ), but before the power amp.

For the 20 HZ signal, I don’t know if it will do and I usually don’t care since the program materials go that low is rare.

If you have standing waves problems you may need to adjust your room acoustic first.