Changes in DAC Presentation - Need Advice

If you are not using XLR connections on your pre-amp maybe give that a try, because many of these new dac companies favour XLR, but I'm still sure it's a break-in issue.

For $200 from Audio Advisor.... I picked up a Audio Quest PQ2 Power conditioner...It changed the sound dramatically on my 10 K rig. Best upgrade and affordable. You could have surge problems which this unit will also take care of.

Get a Border Patrol Dac, made in USA. Sophisticated choke input, tube rectified power supply, produces the most natural, un-digital sound possible. The BorderPatrol DAC uses a R2R DAC chip with no over-sampling and no digital filtering. It is available in several upgrade tiers depending on your budget.

https://www.borderpatrol.net/dac/

As stated by many, a slow subtle change is what you would expect from burn-in or power.  You would also need to turn the unit on and off.  A momentary change, it sounds bright and then it sounds smooth or vice versa can happen once or can happen each time a unit hits temperature.  This usually happens with tube units but in a SS device that is on all the time, it has to be a sudden change in what is being fed to the unit or the unit is defective.  

Power generally doesn't have sudden changes.  One exception might be if your air conditioner is going on or off or some other unit that requires huge power.  This is often accompanied by the lights dimming for a second.  

I would be biased toward some other problem if a Mac Mini wasn't involved.  I have had so many customers have bizarre problems (DAC can't get IP Address, Cut outs, noise, skips in certain tracks, etc...) with Mac Mini's that I am prepared to believe they can and will cause any issue.  

An easy test would be to set up your server on another computer of any sort and see if the problem goes away.  

My MacMini (and all MACs I have had) are awful. I had to buy a cheapo DELL to move my ROON CORE off the Mini. Just too many problems. I do not know how people put up with all the issues I see on Macs. 

Recently ROON had some hiccups for me. I did see 3 software updates from ROON that seemed to have fixed that for me. My music would stop periodically.  So, make sure you have updated all the ROON software to the latest and greatest bits.