I'm trying to achieve as flat a response as possible between my speakers (Polk 6005 sats) and my subwoofer (dayton 10 inch), with an onkyo 502 driving the speakers. The subwoofer is hooked up to the lfe pre-out. (Yes, I know, it's unusual, and Polk does recommend using a Polk subwoofer, high level outs, and speakers set to large. Tough. I want LFE, and Polk's entry level sub only goes to 50 Hz). I've been using a radio shack spl meter and Audio Toolbox OSX on my iBook with a Sonica SPDIF interface. Any suggestions for flattening the response? The dip at 140 Hz is particularly nasty.