I don't believe that the tool and it's general operation changed at all from version 2 to version 3. It did "disappear" from the application and from The Exchange for a short time early in version 3 due to compatibility issues with the new version, but I think it works exactly the same way. If so, that may be why there was no additional documentation published for it if there isn't any.
Making soundsets that include presets and samples has always been a little tricky with that tool. The main thing to remember is to source the samples for any presets that you build from a mounted soundset, otherwise when you make the real one it won't be referencing samples from the soundset, it will still be referencing the samples from the original hard disk location.
Generally speaking it should work like this...
- Collect all of your samples into a folder.
- Mount that folder as a temporary sound set. Pick the name that you'll use for the real soundset.
- Open Impact or whatever instrument it will use and drag the samples in from the mounted soundset to build your kit.
That last part above is important because the file location references are literal. To be self contained it has to reference the samples from the temporarily mounted soundset, not directly from the hard drive.
- Once the kit has been created, save a preset.
- Test the preset by maybe unloading Impact or whatever and open the preset to make sure it's ok.
- Unmount the temporary soundset.
- Put a copy of the preset file into the same folder where the samples are.
- This time instead of "mounting" the folder as a soundset, make a real soundset.
If that process above doesn't work for you or is in some way not entirely accurate other users can follow up on this.