Back when I bought my original surround sound setup there weren't the complex and sophisticated subwoofer crossover settings / small large speaker settings in most receivers / pre amps. Now that I am getting the 990 I have a few questions on this operation. First, I know that the crossover settings can be set in the 990 or usually on the subwoofer itself. Which way should it be set? Which one is better? It seems from my research that the subwoofer settings are many times more specific and apply the changes at smaller intervals. Second, I'm assuming if I have bookshelf type speakers that I should set the speker selections to small. My understanding here is that the small speker settings should be chosen if the main speakers don't have much output below 80hz. What if my speakers are bookshelf but go down to 55 hz? Do I just need to play around with all of these settings and see what works best? What is the conventional wisdom for these types of changes?

Set the crossovers on the 990 - the settings on your sub will only affect the subwoofer itself, and it's best to either disable the sub's crossover or set it as high as it allows.

Unless you have absolute monster speakers, you'll want to set all of them to small - tower or bookshelf. You can tell the 990 what crossover to use based on the response range of your specific speakers. This thread may help you decide how to set the crossovers.