Just want to weigh in here with a real-world (and cost-conscious) example. I have a circa 1994 Sony CD changer and a 2001 Toshiba DVD, both well-rated at the time but under $175 machines. On my Yamaha AV receiver, RX 1105, I can hear a major volume difference (higher on the DVD) and slight but noticeable tonal differences between the two machines. Basically, the dedicated CD sounds better -- more bass, more range, less harsh. Just barely, but it's enough that I don't want to purchase a new DVD-CD universal player, but will stick to the distinct CD and DVD player route. Just one example, but in this case, it seems, the 2001-era DAC in my receiver is not, for whatever reason, delivering quite the sound quality of my 1994-era CD. And this is listening on old bookshelf speakers.
