As far as I can tell the SE version came out early last year. I've read some feedback saying it was a pretty big improvement but hard to know for sure. I think those were people who sent in the original, and got it back with the upgrade, so no chance for direct comparisons. Looks like they upgrade the clock and also the analog circuitry to extract more from their proprietary DAC.
I think if one can afford something in that range it might make sense to just go to the top SE model. I guess it is easy for me to spend your money for you though!