It looks like to me your receiver (the Onkyo) doesn't have pre-outs for most of the channels. If your intent was to add more or better power to your various speakers, you probably can't do that with that receiver. In order to run to a power amplifier, the pre-amp or receiver needs to have "pre-outs" associated with the channels that you're trying to run to the power amp. Once you have the "pre-outs" on the receiver/pre-amp, you use RCA cables like has been previously mentioned.
Sorry the news is probably not in line with what you were hoping, but I think you might have a bit of a case of "You can't get there from here."
Sorry the news is probably not in line with what you were hoping, but I think you might have a bit of a case of "You can't get there from here."