Ghosthouse:
I'm taking a stab at this so bear with me until someone more knowledgable chimes in. I think it is a combination and quality of things that bear on the playback.
I've heard my DACmini out of a top of the line Ayon CDP and it was a bit better than the Ayon by itself.
I tried it out of my TEAC PD-H600 and it, too was better than the TEAC by itself, by a wider margin.
The DACmini out of my iMac with Bitperfect (CAN'T forget the add ons) sounded similar, but better, than with the Ayon and much, much better than with the TEAC.
This all leads me to believe that the transport is the culprit. Every time that CDP spins and reads, its never the same. It can't be replicated equally, every time. But with an iMac (or PC based) hard drive or SSD, its the same read every time. All of that without the spinning platter and laser read of the disk.
I remember reading a review over at 6moons.com about how the reading of a disk and transfer to the DAC, in a CDP, is still an analog (mechanical) function or something to that effect. Its not really digital until the conversion. With a computer, or computer based server, its digital (not mechanical) through and through. I hope I've remembered it correctly and I hope this helps until someone with better skills and background can explain.
All the best,
Nonoise