You should be aiming to play the tapes once only. If you have something that can physically play the tapes without damaging them, make the highest fidelity PCM

You should be aiming to play the tapes once only. If you have something that can physically play the tapes without damaging them, make the highest fidelity PCM (digital) recording possible of the analogue signal, without any regard to further decoding. The tapes should then be placed in a safe place and never played again (unless you later find something wrong with your PCM capture of the analogue signal). Make a backup of your digital/PCM recording and put it in a safe place. All further decoding work is then done using a copy of your high-fidelity PCM/digital recording of the analogue signal.