The OSD ATM7 is a speaker switcher and does not equipped with "Impedance Matching" feature, to be safe you can select to power one zone only or your receiver
might go into protection mode.
If you want to power 4 zone at the same time, you need to install a Impedance Matching Volume Control to each zone.
Or use a Impedance Matching Protection Speaker selector like the OSD ISS4 instead of the OSD ATM7.
https://www.osdaudio.com/products/speaker-selector/single-source/iss4.html
If you want to power 4 zone at the same time, you need to install a Impedance Matching Volume Control to each zone.
Or use a Impedance Matching Protection Speaker selector like the OSD ISS4 instead of the OSD ATM7.
https://www.osdaudio.com/products/speaker-selector/single-source/iss4.html