Crossover Freq.

[htfan14]

If my speakers (mains) have a freq. response of 37hz-20khz and the sub has a freq response 28-120hz what is the best crosover to set the rec. at? It's only adjustable ay 80, 100 and 120. Also, is it better to crank the crossovers on the sub up and allow the rec to crossover? Or try to match the sub to mains?
Dumb questions to most I'm sure, but I just have not been able to get my head around the crossover situation and I feel like there is a "hole" (for lack of a better term) in the sound.
Any help is much appreciated.

[enrique]

set speakers to small,crossover on sub all the way or disable it,set receiver crossover to 80.Thats how i would do it to avoid the double crossover.