I have a Onkyo TXSR-600 and a Polk Subwoofer. I have the sub running from the SUB PRE OUT on the receiver to the LFE unfiltered jack on the sub. The receiver has a sub woofer filter and so does the sub. What should I do? I have the frequency in the receiver set to 120 so that I can let the filter in the sub do the work. Is this right? Help!