You have to listen to different transports.
I tried a Pioneer Elite DV-47Ai for 300+ hours and it was blown away by my Cary 303 -- more refined high frequencies, deeper/tighter/more tuneful bass, a fuller more natural midrange, more expansive as well as more precise soundstaging and imaging and, generally, better musicality. This was using a Bolder/ART Mensa DI/O as a dac and some good power conditioning.
When I switched from the Cary to an old Toshiba dvd player, the music was harsh, disjointed and nearly unlistenable. It was much improved after I dampened the entire transport mechanism with Blue Tak, added a set of isolation footers underneath and mass loaded the player from above with a solid wood chopping block (with Vibrapods in between).
Perhaps someone who has a better understanding of the science can explain how these mechanical tweaks improve the quality of the data stream.
You may also want to read up on jitter -- this is the term for timing errors that are present when data is read off a disc. It is impossible to totally eliminate it. And, to give you a sense of how small errors can have an impact on sound quality, jitter is measured in pico seconds.
