I think the ES has a better overall soundset than any other hardware board I've ever played. Going only by what I've heard on demos and user songs from the SD1, I disagree with Dan's assessment of the ES vs the SD1 ( although the SD1 sounds fine to me ), but we also must realize that Sounds are very subjective.

If quality sampling is the main reason to get another instrument or piece of equipment, while the ES allows for 512 mb of sample ram, I would instead recommend looking toward a dedicated sampling unit, either hardware or soft, particularly since you don't care for the ES soundset.

AJ