If you run all speakers large, you truely are working in 5.1 (or 4.1 in your case)...the sub is ONLY getting the LFE channel signal that the designer designated for the subwoofer. In rare cases, it seems mostly with DTS movies, that low frequencies get sent to channels such as the surrounds and center channel. I assume this to be because movie theaters are equipped with speakers that can handle the full spectrum more efficiently. But home theater isn't designed that way, which is where the small speaker setting comes in. The subwoofers only job is to handle the low end. Basically the ideal setup is to cutoff your surrounding speakers for you subwoofer to take over the low end omnidirectional Hz range. Meaning you wouldn't know what direction the bass is coming from anyway, so why not send it to the speaker that can handle it.
What this means in an envirnment where all the speakers are set to small is...the subwoofer is getting it's LFE signal, or .1, from the DVD...PLUS all the low end frequencies that are channeled to it by the crossover in the receiver. Eqauting to a lot more low end activity than if all speakers were set to large BUT still getting all the sound we were intended to hear in the theater. So, speakers set to small is really the best way to get maximum impact out of your home theater.
Also, I sent and email and have called Harman Kardon seeking answers regarding what is/maybe really going on when the speakers are set to small on their receivers. They didn't have an answer for me when I called, so he told me to send an email and he'll pass it along to the technicians.
