thanks for all the info guys. Even though my fronts are not small set them to small anyway? I read I should do this but dont quit understand it. Whats the point of having towers then? I might as well sell them and get bookshelf then. To me it seems like they would sound no different than bookshelfs if set to small. I dont know. Guess I dont quite understand the concept yet.
OK, we get signal and mainscreen turn on!
Here is some education on audio frequencies. The average human hearing range is 20hz-20,000hz (more oftenly written as 20hz-20khz or Kilohertz). Subwoofers augment the lowest bass frequencies that your other speakers typically cannot, and it has a dedicated amplifier designed to produce the dynamic power needed for true low end bass. A true subwoofer is one that reaches the audible depths of 20hz, which is more felt than heard and is not localizable. I believe localization becomes difficult around 80-100hz, meaning not able to determine were the bass is coming from. This is good because most people only have one subwoofer and don't want to know were the sound is coming from.
Subwoofers have cross-overs and receivers have cross-overs, the process of adjusting them is called "bass-mangagement". Typical Subwoofers have variable cross-overs that can be adjusted from 40hz on up to 200hz (hertz). The reason we adjust the cross-over on either is to have the subwoofer pick up the frequencies that the front speakers can't or don't need to play. The receiver most give the speakers more power for lower bass, so reducing the amount of bass they are playing reduces strain on the receiver's amplifiers, allowing the receiver to give more power to the other frequencies.
Setting the cross-over in the receiver to around 80hz, setting the speakers to small, and setting the subwoofer's cross-over to the max setting (typically 200hz) will allow your receiver to rest easy and get rid of bass cancelations from multiple sources of the same frequencies (i.e. your sub and speakers).
I think that about covers it.