Why not compare the sound of the DVD player outputting digitally versus the Cd player. It is likely the DVD player has cheap analog outs because they are unnecesary to anyone who actually wants good sound. Most people with the ability to good sound would just output using digital not analog.

It is likely your CD player has better analog outputs than your DVD player. That is why most DVD players are so cheap, they are meant to be digital transports, not analog converters.