Bugai : "Fix each preset manually this is an extremal variant.
Convert all flacs it is not difficult of course, but (if i understand correctly) need also *.sfz fixed.
And this process is not so easy to automate."
With
grepWin, it takes just a few seconds. Just tell it to replace all occurances of ".flac" with ".wav" and it will fix everything in one shot.
I'd make a copy of your folders before playing with them.