Re: Old tuners, modern equipment?
Probably not the easiest to do. Go with your ears: remove the Marantz, replace with the Sony, press on.
From what little I could find on the net, both are microprocess controlled. Reprogram the processor? my official language is solder. Change, listen, enjoy, find a new home for the Marantz. Maybe the last option would be to send the unit back to Marantz, with documentation of your grief. Pricey!
May it be in your power to make it a good day: John Isles