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

What's the difference between a $2 cigar and a $10 cigar?

Exactly $8.

Find a dealer with a satisfaction guaranty and compare the units in your own home and in your own system is my conclusion.. Opinions and recommendations will be all over the map.. There are too many variables in systems and environments, not to mention the audio experience is subjective..

Listening in your system and in your home is the only way I know of to find truth for the customer. Forums quickly turn into "makes no difference and you are waisting money" to "makes the world a better place to be, and my unit was a godsend".. Either way you need to hear for yourself..
Magazines, forums and audio shows can help people find interesting gear to evaluate, but other than that, the opinions on most any topic, are so inconsistent to be useless.. You can read 1000s of responses and end up right where you started without a clue, until its in your home and system. Thats just a humble opinion and you know what they say about opinions... In your home, in your system. Trust your ears. The rest is irrelevant.. The BS marketing and, I can hear better than you do, down to the chocolatey sound of a copper wire is all fine, although almost unless when buying audio.. Only way to sort the BS is with your own ears, in a known system and environment like home. Surely people give honest opinions, I'm just saying that a consensus on a subjective subject is not likely to happen.. 

The blithely made responses from roberjerman and others are an illustration of what is wrong with chat rooms - often no context for the comments, evidence of limited experience by the writers,  unproductive negativity and often no humble opinion. Julian Hirsch, the famous (some would say infamous) reviewer from Stereo Review magazine back in its day was often quoted as saying there was no difference in the sound between properly functioning amplifiers. He never commented on the so-called quote during his tenure as a reviewer but he was interviewed after he retired and corrected the misunderstanding by saying he had said HE could not hear any difference.
It is absurd to claim there is no difference in the sound from a Sony Discman versus a Theta transport and d to a converter just because YOU can not perceive the difference.
For the record, I have been in the audio industry from fifty years as of this September and have a lot of experience and in my experience I have never heard two CD players that sound identical even if similar in price. Remember, a CD player "makes up" all the sound at its outputs as it sees fit through the complex conversion and filtering process fraught with design pitfalls that are expensive to address in the design. (And there is no music on a CD.) Also for the record I have a rule of thumb that in order to make a categorically better sounding component the price will often be nearly double the price because you can't just make a whiff of a change but need to raise the level of all the subsystems in the component. Thus the price of a better sounding component gets higher rather quickly as you go on an expedition to find "the best." Such is life.

I pretty much stopped reading when I came to, “For the record, I have been in the audio industry from (sic) fifty years as of this September and have a lot of experience and...”

For, the record, I said my Sony Walkman sounded better than a (stock) high end player. 

So much to say here. I’ll avoid the direct comparison because that is very brand dependent and no one has heard most stuff. but the question"what makes one better" is, to me easier to answer. A CD player, end-to-end has many components, and many of those are analog or have analog components - including those before the DAC!

My broadest comment is to migrate from CDs to files, and play them out over USB. For me, using ALAC/FLAC, either ROON or Bitperfect streams sound substantially better than the original CD - played through the same DAC and equipment. In my experience, the best sound and lowest noise  requires running my streaming hardware (and OLD macbook pro) from its battery, not plugged in, sigh. Why better? Likely jitter. A CD transport following the standards probably puts out SPDIF, and a cheap transport - or even a good one - will have some timing degradation.

Note as i have blogged about, SPDIF makes the source (e.g.: that cheap-o CD player) the clock. Your $10k DAC takes jitter form the source.  USB turns this around and simply sends bits to a buffer, where they are re-clocked by the DAC, or can and should be.

Once you have the bits in the DAC portion of the chain one must re-clock very precisely and eliminate noise, both of which contribute to jitter. Jitter, changes the X-crossing point of the reconstructed musical wave and therefore is a plain, old analog distortion. no audiophile magic necessary here. next come all sorts of noise and power supply related opportunities for distortion and of course, the reconstruction filter and analog preamp that is the end of a DAC’s internal functional chain. So if you think capacitors, preamps etc make a difference guess what, you have several of each in there. They must be good.

Bottom line, there are lots of places a transport and DAC can mess up sound. The chip architecture, which most focus on, is probably the least.

Now, just to contradict myself, i have four DACs and have had the chance to borrow several more in my very revealing system. From a Schiit Mido3 (the best $99 DAC i can imagine) to a Theta DSPro/G2 to a ridiculously re-worked MSB (all rework my own designs) these do NOT sound the same - so the comparison of the cheapo to the Theta simply proved that someone can’t hear or has a mediocre system. Ar these differences night and day, awful vs glorious? No! That’s a huge issue in this field/hobby, crazy exaggerations. But the differences are real and manifest themselves even more over long periods of time. My gold test is always "can I go back without missing component X?"

BTW i heard the effect of a $40 amazon sourced Toslink-to-coax SPDIF adapter. You just cannot imagine ho distorted it was. and I have pics of the resulting, ugly wave when i used it in a test jig with test tones (files) and a ’scope. UGLY! Clearly visible jitter to the naked eye! Step function jaggies in the sine wave! Ugly!

Hop this helps
G