My digital front end is a SGC i9 based optical server to an Optical Rendu to a Holo May KTE.
The May is extraordinary. I have tried using both I2s and USB, the USB was better to my ears.
My digital front end has undergone many changes over the last 7 years, one thing I can say for sure, is that up-sampling or DSD conversion is done much better on a server that is designed for it rather than the DAC.
In your case, the iMac Pro has the same issue the Mac laptops have, which is interference from the display (the laptops are even worse). If you really must use a Mac, you will be better served getting yourself a Mac Mini. Better yet is something running a Linux distro (no, I am not a Linux fanboy) meant for audio. One of my iterations before my current set up was using Daphile, and it was very good. I suggest rolling up a Daphile server on an old PC and test driving it before you change your DAC. You can still use Roon with it.
Roon is a pretty decent music player, but Daphile is far and away better. Better yet is to use HQPlayer Embedded (which is what I use now). Daphile is painless to set up, combined with Roon, you get a very good music player that will compete with anything. Setting up a Linux server with HQPlayer Embedded is no simple task, and only a few commercial servers are sold with full support for it. The learning curve with HQPlayer is not very steep, the issue is the plethora of options means you will spend months switching between things until you figure out the best combo - not much different than tweaking speaker positions.
Small Green Computer sells a number of servers, all of which can run HQPlayer. I went with the i9 server so I could do big DSD conversion.
If I had to do it again, I would not bother, I have found I prefer a mild up-sampling of 4x with a 20bit depth as the sweet spot in my system which can be easily done with an i3 processor. Sometimes I switch to DSD 512, and I am awed for a couple hours at the "clarity and airyness,’ but then I start to find it fatiguing. I can listen to 192/20 all day.
One last comment about DACs that people do not consider enough.
Pay attention to the output voltage, it can limit you on what preamp you want to use. The May (and many other expensive modern DACs) output about 5v instead of the traditional 2.4v. This will cause major crosstalk issues with gear with poorly designed and outdated circuit boards (the Carey preamps are a fine example of poor design and worse customer support). Many tube amps will not be able to behave well with a 5v input. Most SS preamps will be OK with it.
A higher output voltage on the DAC greatly reduces the noise floor, so it is good from that end, but it means that you need to either use a low gain preamp, or reduce the output at the server side which has a direct impact on bit depth vs noise floor.
After several years of trial and error, I wound up using a Levinson 523 preamp. The output level on the May was a real issue for me, I wanted a tube preamp and had trouble finding one that fit my system and could handle the voltage.