The way to do this is to set the volume of a zone to straight pass through, and save that as the default value. Then make sure the control system doesn't change it. In other words if you're using an AVR as the zone's volume, you should not have any problems because no volume commands will be sent to the ProAudio switch.
To set the volume to straight pass through, and then save them as the new volume settings, use the "VZ" and "SS" commands. Assume we want to set zones 1, and 5-8 to pass audio straight through (no gain / no loss):
- ^VZ @1@5:8,200$ ; set zones 1, and zone 5 through 8 to 200 (200 = Pass audio straight through)
- ^SS 256$ ; save the current volume levels as the new power on defaults
The "SS" command saves all volume levels for all zones, so make sure all your zones are set to levels you'd like if there's ever a power failure. When power is restored, these are going to be the levels the zones are set to be default.