The OX is not a realistic load. It uses the same technology as the Two-Notes stuff. Your test was inherently flawed. There will be FAR more low frequencies with the OX as the OX uses a simple RC filter for the impedance curve rather than an RLC filter like our own LB-2 or a Suhr Reactive Load.I have made many tests, the most representative was when I used the real amp into the Universal audio OX and send the fractal also to the OX through the secret line input it has. In all the tests we made various amps ans preamps, we always noticed about the same results: There are some low frequencies in the amps that they cannot reproduced ( we tryed many eq tweaking) with the FAS and they have a big impact in the feeling that the guitar player has in his hands.
An accurate test would be to use our LB-2 loadbox and use the LB-2 impedance curve for the model.