The built-in subs are often hooked up to the subwoofer ourput of the receiver, at which point it's little different from any other system with a subwoofer - set the speakers to small, set the sub to on, and pick an appropriate crossover point. The only difference is that you have to use a splitter to divide the subwoofer output. You can also skip the subwoofer connection and just use the binding posts like a normal speaker, in which case you may want to run the mains as large. I'd hoped to find a user's guide or other info on DefTech's site, but came up dry - there's no good setup info and the specs aren't clear on where the speakers transition to the powered sub.