Today I´ve found an interesting video of the original Z Wreck model. The guy showed how the amp sound changes when the volume knob increased.
https://www.youtube.com/watch?v=nv82b0sLmEU
At 11:10 he turned the volume up and the amp began to distort.
I´ve tried to achieve a similar sound with my Telecaster but I can´t get it to distort even if I put the input slider at +15dB. I have to put the "Slash" booster in front of the amp and raise it fully (+20dB). Is this normal to boost this model with +35dB to get a similar distorted sound? My audio interface gain is set to 0dB.