Audio quality difference between DVD player and CD player

It's not that simple, really. Specs can only tell you so much about the sound of a piece of equipment. It is not true that 192/32 DAC will be better than a 96/24 or even a 44.1/16. The spec only relates to the DAC, whereas the sound quality is the sum of several factors, of which the DAC spec is just one part. a lot of people will tell you, a small one at that.

A dedicated CD-player will pay a little more attention to power supplies, layout, keeping the analog signal path clean, short and free from noise. It is a dedicated machine that does one thing, so it suffers from less compromises.

A DVD player will also have high-speed video switching and decoding circuitry. High-speed circuitry tends to dump switching noise back on to power supplies, and this (probably) affects the audio output quality.

Cheap DVD players generally have all-in-one VLSI chips to save space and cost, only using a separate set of opamps for the final audio filtering. This may compromise the audio quality further.

However there are some fantastic compact solutions from TI/BB for all-in-ones, and the quality has the potential to improve markedly. LT has introduced very low noise power supply regulators that are built to generate lowest possible noise, comparable and even better than super-regulated linear supplies. How long it takes for those to hit players only time will tell. There are some DVD players with a lot of modding possibilities that bring them near CD player quality (and surpass cheaper components), but those are only for the DIY types.