You can always run it in between a particular component and the receiver using line or tape but you would not want a simple analog graphic equalizer, especially an inexpensive one, for the whole system anyway. They usually introduce more problems (like noise & distortion) than they supposedly cure. Parametric EQ on the other hand can be helpful when done right.
I used to use an EQ from Radio Shack with my older receivers and enjoyed the tweakability with my room issues. But now with a Modern receiver like the HK 635 with Room EQ built-in, there is no comparison.