Are you suggesting that your E88CC DAC becomes overwhelming over time?
I am not suggesting this, or is it a experience I have had.
I have experienced E88CC / 6922 Tubes from a desirable vintage during Tube Rolling that can screech and is an immediate repellent when compared to other Tubes during the rolling experience.
In relation to your post sharing the info' about the demo' you have had.
I'm suggesting your demo' received has left you having perceived a sonic trait.
I do not know if this was as a result of using the DAC in your own system or on another.
It is hard to determine if a demo' is not carried out in the home system, if a detected trait will become more noticeable, maintained to a similar presence, or blended to a lesser presence. The buyer has to live with their decisions made, the musical encounter that is able to be created, is for the best one that is able to be experienced for long periods, not feeling the need to shorten the experience as a result of a sonic being produce by a particular device prematurely causing a listening fatigue.
Hence I suggest that now the trait is known, it might be for the best, if an experience is had with a few others models to see how these leave an impression.
Hence, Caveat Emptor, or Buy in Haste, Repent at Leisure.