Maybe this will help clear up some things:
You need 2 downloads, the App itself (MIDI Song to Style) and the Voice List (folder of several .txt files for different keyboards)
They are zipped files, so unzip them to where you want them stored.
I did not see this under the PSR-SX900 downloads, for now it's only under the Genos 2 downloads.
So install the app, and by Default it will be using the Genos 2 Voice List. For other keyboards, you then go to the Edit menu, and select "Import Voice List".
At this time, it allows you to import for Genos, Genos2, PSR-A5000, PSR-SX600 / 700 / 900. (Nothing for the DGX-670, at least not at this time)
It says to use a sampling rate of 44.1Khz, but I happen to be using 96K, and works fine with the SX-900. I can also Save the Style directly to the SX-900, or to USB drive.
Jerry