If you have to set all channels to the same frequency cuttoff, and if you do not have any surround speakers (if you do, you should tell us what they are), you should set it between 60-80 Hz. Although your main speakers are at -2dB @ 45Hz:
http://www.paradigm.com/products/paradigm-reference/floorstanding/studio-series/studio-60
Your center speaker is at -2dB @ 55Hz:
http://www.paradigm.com/products/paradigm-reference/center/studio-series/studio-cc-590
You should set the frequency above 55Hz, and probably 80Hz would be best for it, so that it is not going to strain when playing fairly loud.
Your speakers should all be set to
small, and if you can select different crossover frequencies for the front center than for the other front speakers, you may set the crossover lower for the main right and left channels than for the center, but there is no need for that.
Basically, the ONLY time you don't want to set all of your speakers to
small is if they can go as deep as your subwoofer. Since that is almost never the case, it is almost never a good idea to set one's speakers to
large.
You see, the idea is that you want all of the frequencies to be played, no matter what channel they are in, and so if you don't redirect the deep bass from the various channels to the subwoofer, you do not hear the deep bass from those channels that is below what your non-subwoofer speakers can do.
In other words, if you set everything to large, the center bass is going to be lacking below 55Hz, and the main channel bass will be lacking below 45Hz. Not only that, but when playing loudly, the bass drivers in those speakers will distort more, because although they are not giving you much output below those frequencies, they are still being asked to do it, and so you get extra distortion that you could avoid by redirecting the deep bass to the subwoofer that can handle those frequencies.
