The higher end model offers both 3D compatibility and DACs for improved audio.
The folks at Yamaha have a pair of new Blu-ray players available now, both of which give you Netflix and Pandora, both supply you with USB ports for hard drives and the like, and both have FLAC playback capabilities. What separates the $329 BD-S673 from the $229 BD-S473, aside from 3D capabilities, is audio.
Only the S673 offers you built-in Wi-Fi, DivX HD Plus playback, analog two channel mixed down output and, most importantly, a 192kHz/24-bit DAC for much higher quality audio. Both players are available now.
Source: Electronic House