Thanks very much for the honest and thorough reply.
You have confirmed what I suspected about the S1000's transport: It's the same, but different. Given the significant price difference between the S1000 and the S2100 some compromises would have to be made besides the downgraded DAC. I've looked at photos of the innards of all three players, and there are differences in parts and architecture. The S3000 and S2100 are the more premium, the S1000 somewhat less so. That said, compared to other players in the $1500 price range, the S1000 is built like a tank.
I'm taking your advice and going for the S2100.
Thanks again!