DAC nuances

newer isn’t always better

my musical fidelity trivista 21 tube dac from 2004 still holds it own against some five figure dacs I have auditioned

just like a wonderful french dinner was tasty back then, as it is today

Different companies have different sound quality objectives... normally called house sound. SO, it is easy to conclude that an old something sounds better than new by dipping into a different house sound. Typically the sound within a company has improved dramatically in ten years. So, it will be a question of comparing similar house sounds. 

I recommend posing your system and thoughts into ChatGPT or other AI... adding comparisons and contrast sonic characteristics.. Generally it is really good at characterizing sonic characteristics and leading you the right way. 

A lot of new high end digital leans analytical with trying to give a listener maximum detail retrieval. Your old Esoteric player was designed to play CDs and make them sound as natural as possible. I would bet latest Esoteric is more analytical and less engaging than your 13 year old player. Keep it. 
But if you’re auditioning DACs try to find a dealer who has Meitner MA3i. I find it both detailed and musical. 

In the past 10-15 years, DAC manufacturers have been focused on features (sell! sell! sell!) that have become prominent in digital circles - namely digital signal processing. Filtering noise, equalization, and to some extent clocking (to bring out more detail) are the said features that were born under specialized DSP. Lately, the clocking aspect has been focused on jitter reduction as it is low hanging fruit when it comes to better sound at minimal cost.

Flagship DAC's of old tend to age well. IMHO, DAC designers of old focused on actually listening to their gear to ensure a non-fatiguing sound that was well-rounded and pleasant. If you have good all-around speakers, that is likely evident to you, and has grown on you. That sonic character is what they sold then. Now? Kind of akin to home theater, DAC's- like transports- are all about the features as mainstream steers towards a focus on selling attributes instead of polishing sound. It doesn't help that there are only so many chipsets available in order to create a house sound; which has made many DAC's sound similar - if not identical when some of those features are duplicated across manufacturers.