Why don't Omni-4000 controls (PB-2 - PB-6) show up in the Auto Search in the toolkit?

Why don't Omni-4000 controls (PB-2 - PB-6) show up in the Auto Search in the toolkit?

The Auto Search does not find the older Omni-4000 controls (PB-2 - PB-6). It will show any PBX-10, PBX-11, PBX-HMC or AutoSort controls it communicates with though.