hi all bro and sifu sekalian,

I am having some problem of connecting my head unit (one pair of RCA) to 4 channel amp.
Act, my set up was done by one of the so called sifu at my hometown and he said dat his set up is damn superb whereby his set up with only 8 subwoofer is able to cover another competitor with 12 subwoofer.
If found out a lot of setting being done wrongly by this guy. I am using this 4 channel amp to run one set of component at one subwoofer.
He used channel a for the component set and channel b for the subwoofer. I found out that for channel b (subwoofer), he chose the setting as off instead of LPF. Act, which one shud be the correct setting for subwoofer? LPF or off? In my opinion LPF shud b the correct setting after going thru ice forum in lowyat.
I have drawn two drawing for ur reference. Currently, my set up is connection A but I feel that connection B should be more appropriate.
For connection A, i will be getting mono instead of stereo bcs he is connecting the rca (right side) from head unit to channel A for left and right sides.
So, which one shud be the correct connection? Connection A or B?
Thank you very much for the help!!!