Solved, more or less.
After talking with a number of Yamaha service folks, the consensus is that the db values should be extremely close within the same model number and particularly within the same production run (it's an electronics issue). There could be variation between models but it should not be that significant. Between manufacturers is anybody’s guess. That said, within the same model, the audible output should be indistinguishable if the two units are utilizing the same base configuration and sound program. Between models, base configurations plus sound programs of the same name can produce different audible outputs and they can be fairly different. There are other configuration factors at play but there is little value in going into those now. So, the recommended procedure was run the system initialization on both systems (which didn’t change the situation) then run the firmware update on the new system (as the old system didn't need an update). This last bit worked reasonably well. The systems are now fairly close in output on comparable configurations and programs.