In most cases, adding an external DAC box is redundant, and introduces more noises, cabling, connectors, circuitry etc.. You will get ALOT more performance with the mods to the players internal DAC/Analog output section versus adding an external DAC box with stock circuitry. Plus you need to spend extra money on power and digital cabling, for what? a small improvment in sound? The mods bring a ton more improvement across the board (and minialize circuitry as well) for considerably less money spent.
Modify Oppo 980 or add External DAC?
Will adding an external DAC to an Oppo 980 bring the same type of audio improvement as internal mods?