Best subwoffer crossover with room correction

I have a Rogue Stereo 100 Dark amplifier and Vandersteen 2ce Mkiii speakers (-3db at 29 Hz). I use an Icon LA 4 preamplifier. I have an 1. An SVS 300 subwoofer, 2. A Triad q3 inch, 700 wat subwoifer, and 3. A Snell 18 inch subwoofer with 499 watts amplification.  . I  tried to  use the REW Software and the parametric SVS 3000, but could not obtain a smooth bass frequency response. I think I need a crossover at 70% below the lower limit (20 Hz), it will not overlap with my main speakers. So I am wondering if anyone has a recommendation for a good crossover for my subwoofer. I know that the Vandersteen Sub3 is designed specifically for my purpose and may be my best option.