I loaded the same ir files into other things like bias amp 2 and pedals and they sound great but when I load them into gfx they sound muffled. The built-in cabs sound fine.
Could you please send us your ir files here: support@tonelib.net , so we could investigate on your problem?
i can report the same thing. Every IR response I load sounds far more muffled than all the built in ones.