Pre-outs/main ins with jumpers....SUB connection?

With the does one connect a sub?
Some subs accept the ins of your speaker wires taking the signal from them & forwarding the uneffected signal on to your speakers. If these are not present remove the jumpers then maybe you can use a pair of Y connectors connected to the left & right preamp outs using one set of L+R for the sub and connect the other L+R set back into the main ins.