Hello @Akessel89 and welcome to the forum!
I am I right in that you want to use the PS-100 100% as a load box and you do not want it in the attenuator loop?
This is possible! You can treat the PS-100 as a silent speaker, just programme the ZMACS with the AMP IN impedance. For example, set the PS-100 AMP IN to be 8 Ohms. Now you have an 8-Ohm silent speaker you can route amps too. From there you can take a line out and do what you want.
But I think a more versatile approach is outlined in the manual in page 14.
Put Power Station in the attenuator loop then it can be applied to all channels and it can be bypassed too with a footswitch. If you set the PS-100 volume to zero then it’s basically a load box.
I hope I understood the question, please come back if not!