The ATA could communicate with only one device without having a gatekeeper.
In order to be able to call three diferent devices, you will need to make one of the devices the “gatekeeper”.
then point the ATA to the gatekeeper , to be able to call any of the three devices.
Look to see if the OS that you have on those 2600 support gatekeeper function.
If they do, activate the gatekeeper, and make the ATA register on the gatekeeper.