There is a bias in your comparaison as stated by the poster above. You are using EQ to enhance the sound on your other boxes.
The output of the WD Live is FLAT. there is no modification to the sound.
I have absolutely no issues at all with audio it is amazing ! However, depending on the type of audio, especially multichannel, it is better to use optical out and listen through multi channel speakers.
Sure the WD Live could use some EQ and advanced sound settings, but I have made some tests with different files and have no complaints whatsoever regarding sound.
I’ve done some testing playing a ripped movie through the WD Live and that of my good old Sony DVD Player, with flat settings, (using RCA out) and the sound is virtually identical, it is far from being muffled, the highs and lows are there.
I’d say even that the quality was slightly better out of the WDLive :) (more rich) in some cases.