Two SB-1000s could get you an overall flatter response and more accurate sound, if you know how to set them up correctly. You can't just get two, and just place them in the most convenient spot, and assume that will grant you a better response. It does take a bit of effort. I don't think that two SB-1000s would have the dynamic range of the ULS-15 or SB-3000 though.
As for the Klipsch RP-600m vs Hsu CCB-8, that is a toughie. I think that the modified tractrix waveguide in the Klipsch speaker probably has a bit better directivity control, but the Hsu's imaging is to die for. The Hsu speaker probably has greater dynamic range too. The Klipsch speaker will likely dig a bit deeper, but who cares when a subwoofer is being used.