A:Answer In Setup, you'll tell the receiver which speakers you have connected. That's when the auto-set-up mic tests the channels and detects the speakers. It will tell you which speakers are hooked up, and whether you have a 2.1, 4.1, 5.1, 6.1 or 7.1 arrangement. Adding another sub changes nothing; it's the same channel running through two subs, sort of like dual-mono. There is no stereo sub channel, so two subs will appear as one sub, though they will probably give better coverage for your room. Also, Large vs Small only does one thing; it allows you to cross-over the speaker's signal to the sub. Set to large, the speaker receives the full signal. Set the speaker to Small, and you have the option to set the cross-over to, say, 80ohms, which is a typical cross-over setting to send anything 80ohms and below to the subwoofer. If all your speakers are set to Large, you may not get any sub signal at all.
