Chris grinderz, if your water is already that soft, you may get away with only using a carbon/sediment filter.
I'm not familiar w/ the S1's, and what was 'new & improved' with the SII. Other than a sintered filter that had to be removed because it was installed wrong at the factory (that is only needed in Europe, but not on US municipal water), my SII has been flawless for going on 8 years.