When a digital device (PC, portable media player, etc.) plays a digital audio file (ogg, mp3, flac, etc.) the audio signal output is always the same, regardless of the device type/brand, am I right? Thus the sound quality should not differ. For instance, I have an iPod that plays an mp3 file. If I play the same file on a different brand media player the sound quality should be the same since it is the very same signal (no equalizers, or any sound alterations).
Is this true? If it is true then I reckon it is only the headphones/speakers that matter as far as the sound quality is concerned.
P.S: all of the answers are really nice! wish i could accept 'em all