Cant replace default sounds?

do you use the app? there you have a defined selection of synth engines to put into slots.

if your using the stuff I guess your are using samples? because synth patches are not really compatible as the opz does not support the same patches, but if you are using the sample based "pacthes" I think you have to change the file ending or something....there was something similar in the last weeke sin this reddit:

.aifc extension to .aif

/r/OPZuser Thread