I don't doubt that some of the older CD players sound worse than the DVD player. It would be a cool test with a high-end CD player from the 80's and the 90's and compare that with a new DVD player. To me, digital all sounds the same.
It depends on what one considers "high end". My brother and I did this test with a Denon DCD-1560 which is generally regarded as a pretty good player (although likely doesn't qualify as high end by price). We compared a Denon DCD-1560, Denon DV-2900, Sony DVPS-360, Pioneer DV-578A, and Music Hall CD25 using their analog outputs and using their digital outputs though a Benchmark DAC-1.
For all tests the levels were matched to within a couple thousandths of a volt at the speaker terminals using a 1kHz test tone.
The two Denons and the Benchmark DAC-1 all sounded too close to call no matter the connection...sounded good and no doubt very technically accurate, but seemed like a cool/clinical presentation, IMO. To us, all of the players through the DAC-1 sounded the same and had that somewhat clinical presentation. Via analog, the Sony seemed to lack some soundstage and seemed a bit too soft in the presentation. Not really dull, but just soft, for lack of better terms. The Pioneer seemed a touch less technically precise than the Denons or the DAC-1, but a touch warmer and perhaps wider soundstage. The Music Hall via analog seemed to be the best sound to both my brother and I. Plenty of detail yet pretty smooth and open with a good soundstage and some depth without the clinical sound.
Those were our subjective impressions. But, when we did some blind A/B testing, neither of us scored very well (results essentially equal to guessing) in a "same or different" type of scenario.
I cannot remember if we used my Yamaha C-80 preamp, or the Proceed PRE (thinking the latter due to remote control for easy A/B switching) but not positive. Amp was Levinson No. 23, speakers were Paradigm Studio 100. Speaker cables were short 12ga zip cord, interconnects were combination of Blue Jeans and Monster.
YMMV....