poor sound quality on DVD digital audio out?

I've read a few posts re. the poor sound quality from the Bravo D1 coax digital out, which said the problem was solved (or reduced) by switching to the optical out.

My question is: since DVD digital audio output is simply a digital bitstream; unless the DVD player has an improperly-designed circuit (too-slow rise times, misshapen waveforms, etc), shouldn't the audio out signal be the same across all players, and the sound dependent on the processor/amps/spkrs? Has anyone experienced sound quality variations/problems with other players?

Thanx.