How to hook up Subwoofer ?

Can anyone please tell me if can I plug main spkers and subwoofer together into the same post of a 2 channel amp?
Will that degrade the sound ? I really don't want to run the signal thru the sub to the mains.
What brand of sub is it. Is it a passive sub ? Active Sub (has its own amplifier)? REL subs are designed to be connected to the amp along with the speakers. You may want to eMail the Manufacturer or a dealer, but you could try; just keep the volume very low at first.
Yo Kitty, There are several ways to hook up your sub. Lets look at line level first as it is the best, and then speaker level. If your receiver/amplifier has an RCA "subwoofer" output you can use it if: the receiver/amp has a built-in crossover to remove the bass to the main speakers. If no crossover is built in to the amp, then look at looping the preamp outputs thru the sub and back to the amp. This will allow the crossover in the sub to filter out the bass and run the main speakers in "almost full range" mode. The sub will provide the bass below about 80hz. If the sub lacks the stereo in/out RCA jacks to hook it up in a line level manner, then you should run your speaker wires to the sub and then run more speaker wires from the sub to the main speakers. This will allow the crossover to filter out the bass and send it to the sub. If you just run speaker wires to the sub off of the Speaker B terminals then you are merely adding bass that may or may not be in phase. Also, you are not allowing the sub to protect the woffers in your main speakers from "popping" or the amp from clipping when listening to the exaggerated movie soundtrack bass. As for degrading the sound, if you are running long (over 15') speaker wires to get from the amp to the sub and then from the sub to the speakers, then yeah try to shorten up the runs or go line level. Even if your runs are long, you're better off using the sub to protect the main speakers from damage.