First off they are sfz format rather than soundfont (sf2) files, but no matter. I;m no expert on this but it has come up a while back, so I dabbled a bit, to get it working.
You need to have the folder with the samples and then have the sfz file in the correct relationship.
I have a folder; Richard Webster – Church Steinway
Inside that are two folders titled ‘Samples’ and ‘Instruments’
The samples go in the Samples folder and the sfz file goes in the Instruments folder. You can then drag the sfz file into sforzando and it should play.
The 9000ft piano is slightly different.
There is the main folder; The 9000ft Piano.
Inside that folder is the samples folder titled ‘The 9000ft PIANO Samples’ and sitting on it’s own is ‘Sid – The 9000ft PIANO.sfz’
You can open sfz files with Notepad or other text editors, and you will find this note from Sid;
Place this SFZ file in the “The 9000ft PIANO” folder outside of the samples folder.
If it loads, you may have no volume. In sforzando, click on the Controls tab and adjust the knobs as desired. There is a discussion about this with Sid somewhere in this forum.
Lets us know how you get on.