Mr Ee
Major Contributor
I believe the pro uses a burr brown chip, the plus uses an akm.A lot of audio reviews on YouTube suggest that the sound of the DAC in the Pro Plus is superior. Both use the same chip, but the other components that feed and power the chip in the Pro Plus is superior, according to all of the reviews that I've seen. I ended up buying the Pro Plus, but it's my first ever DAC so I don't pretend to know. It sounds great though.
But yes, the other components in the plus help.