What Sonically is the Difference between a $1,500 CD Player and a $10K-$25K One?

I recall a comparative test years ago between a Sony Discman and a Theta transport/DAC. A Boulder preamp/power amp were used with Quad 63's. The result: NO Difference! The French chef applauds! 

The difference between an expensive and cheap anything in audio is the exceptional room, set up and gear you need to hear the difference. Without all that the money is mostly wasted.

+1 jafant and wlutke .  Significant difference in sound quality, but without comparable gear and great room certainly not worth it...

In terms of measurable distortion? Nothing.

And its been that way for decades. After some 30 years of using various CD players my two personal favourites were also the least expensive. Not necessarily because of their sound more likely because of my low expectations. I really wanted my far more expensive UK race tuned Sony models to sound better, but they didn't. Even the filters made bugger all real difference.

What you might get instead for paying more are features such as Bluetooth, switchable filters, looks and build quality.

Album art display is pretty cool too.

The difference is with the expensive CD player years later you will be sick with thinking what a great turntable you could have had instead. While with the cheap CD player instead of years it will be days.

With some (not all, not by a long shot, but with some) expensive CD players if you spend enough money you will have the unparalleled satisfaction of having the very best of digital playback of anyone anywhere. Only with the qualifier "digital" of course. While with the cheaper CD player you won't have even that tiny and brief little shred of satisfaction.