Quite frankly, other than perhaps maybe suggested crossover and/or LFE level settings I am not exactly sure what is meant by an AVR "sub setting". Depending on the size of your L/R speakers, the usual crossover is 80hz. The different size drivers in each sub is pretty irrelevant. I have a couple of old Yamaha subs in another system in my house with "dual 8s" that, although they can't be played quite as loud, give me better bass extension than a Paradigm I have with a 12" driver.
Just get the crossover, volume balance between the two subs and phase setting right and you will be good to go.
