i know he isnt using a sub ali bhai. channels 3 and 4 are being used to run the JVC coaxials he has. the switch on an will have the (lpf/off/hpf) folter options for channels 1/2 and 3/4.
in some cases the off is also known as Ap/full but it means the same. no filter.
poster can keep the front comps at hpf and rear coaxials at off/full. the problem is when the volume is turned up and u can damage the speakers.