Power Amp-Cross Over-Subwoofer

If I just need something to act as a crossover and volume control between a separate power amp and my sub, are the Rane crossovers a good bet? I see where they are affordable on Ebay. As far as I know, I just need something that will allow me to adjust the crossover point and volume to blend with my main speakers. My plan is to just run the subwoofer source through it and leave my mains out of it alltogether. I have an Audio Source preamp feeding a Parasound HCA 1200 (or two Marantz mono blocks- depending on how I want to divide the power between my PSB Goldi speakers and NHT2i sub.)
Any suggestions that are inexpensive are welcome:)