looks like the OSM has compensation for impedance so you should be ok just keep in mind your amp was not designed to drive 8 speakers at once (not in home theater mode). so even with compensation it will still tax your amp more as you add more pairs of speakers.
3 responses Add your response
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.