Subwoofer match for Von Sch. VR2

What <$600 (new or used)sub has anyone used successfully for music with Von Schweikert VR2s?
I tried a Paradigm PW2200 briefly but could not get it to integrate well enough. Once the VR2s were fully broken in, properly placed and loaded with lead shot I no longer felt I needed a sub for 2 channel listening.