What it sounds like he trying to do is fudge a 5.1 using a 30 year old pro-logic reciever and a 22 year old Subwoofer+5 speaker set.
Now looking at the JBL manual it is possible to get a 4.1 using low pass crossover by running speaker wire from the receiver to the subwoofer's "IN" clips and...
Well according to the manual for the Sony D515 (a VERY OLD receiver which only does Pro-Logic mind you), the only speakers with inputs for a "Terminal B" are front left and front right. The surround (which is mono) and Center channel have their own set of inputs.
Also this does not support a...