Congratulations!!!!!!!!!!!!!!!!!
First off congrats, on selecting a great set of speakers. How do they sound? Which sub are you using?
You may know all of this but just in case here you go;
The crossover setting is basically how the receiver separates where the frequency is divided between your speakers and you sub. Now the great thing is that your front mains go pretty low in the frequency response area. What you do not want to do is judge where you set your crossover by them alone, as your receiver will then use that as the baseline for all of the speakers. Your surrounds give the response between 65-95 Hz; given the room specifics what you hear would be between these two frequencies. So they are the weakest low end speaker in your set up lets say. Not that they are weak they are GREAT speakers, but their lowest frequency response is the highest HZ number in your system.
When you set your speakers to small you are basically telling your receiver that you want the LFE (Low Frequency Effects) to go to a subwoofer not the mains, center, or surrounds. You then (by setting your crossover) tell it where to divide the signal sent to your speakers and your sub. So it is the most common set-up in HT to set all of your speakers to small, and then set your crossover.
With all of that said I would recommend you use small on all of your speaker sizes in your receiver, then play around with the crossover setting to see what sounds best for your particular tastes.
Oh yeah, sometimes this goes unsaid because we are so busy with our latest set-up and dialing it in, ENJOY!!!!!!!!!!!!!!!!! Take a little time to just sit and soak it in my friend!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!