Uh… Then I mixed this up. Sorry. But somehow I already converted SF2 to XRNI… Maybe with some converter available…
You can try this:
https://github.com/atsushieno/sf2xrni (https://forum.renoise.com/t/sf2xrni/28025 )
Blisshttp://www.discodsp.com/bliss/?l=de
seems to be able to import Sf2 and export SFZ 
Try demo and please report! EDIT: Ah, damn in demo export is disabled. 