Aftermarket radio, subs and amplifier wiring help

Okay, I have made a lot of progress in messing with this truck. What I really need to know is, how to specifically wire my subs up to amp to get a safe and full potential performance? I have a 400 watt peak power 8" Boss 4 ohm dual voice coil sub and a 12" Pioneer 4 ohm 800 watt peak power sub. My amplifier is a two channel bridgeable legacy predator. 800 watts when bridged. I want to hook both speakers up to amp if possible. Some experts say that the peak power rating does not mean much. But I do not know.

Also, how does the wiring from the subs to the radio work? Is that what the RCA's are for? Or are they only wired to the amp and the RCA's are from the amp to radio. Need help ASAP please. Thank you