This has also been my experience with dual voice coil woofers and somehow using those two channels seems to make it a bit more dynamic than when driving with one channel only.
I have owned Bob's Sunfire True Subwoofer EQ...with its built in EQ, passive radiator and 2700 watt amp for many years now...its a killer unit. There is nothing else that can rumble the walls for movie soundtracks or stereo listening. Just got it back after recent repair at Deltronics.