Options to improve digital sound

Mac fanboy, have all their products. However, for music, I do not use any Mac gear, except my iPhone to control my streamer. 

Going to suggest, removing the Mini, replacing it with a quality streamer. Don't change anything else yet. Just get used to the streamer, then go down the upgrade path. 

I had my old ipod (yup, still got one) plugged into my system for a while. It sounded flat, hollow, and compressed. 

Get a Roon Nucleus Plus revision A on Ebay or USAM around $600.00. Upgrade the power supply (s-booster).  $400 or so.  Plug in external hard drive or install internal.  

Use DSP to "tailor" sound.  Use high quality cables, they do make a difference.  You are familiar with Roon.  A very painless way to go.

@audphile1 Roon Core is where vast majority of processing goes on, the relatively complex interface of Roon is processor intensive. CPU's working at relatively high rates creates more noise and higher latency, both are enemies of resolution  Higher latency also means greater chance for timing issues. The reason so many find Roon inferior to the proprietary music players is those music players have been designed as to require far less processing and deliver lower latency, result is both increased resolution and more analog like sound quality. 

As for empirical evidence, I've had a variety of Endpoint and Core streamers, the Cores have a far greater impact on sound quality vs the Endpoints. I'd suggest its both the processor, latency issue, and the fact Core sits upstream of Endpoint. Contrary to certain popular opinion, noise introduced anywhere in the streaming chain cannot be eliminated within the offending component by components  further down the chain, no getting back resolution, latency lost. 

I purchased both the SonicTransporter and Roon Nucleus, but returned the ST7. I found the Nucleus’ software to be more stable. The ST7 had frequent connection issues in just the two weeks I had it. 

Thanks @sns 

I do realize there’s a lot of irrelevant tasks in the mac mini that can potentially impact sound quality by negatively impacting roon related processing. I’ll be trying a dedicated core soon. Can’t wait to see how it impacts the sound hopefully it’ll be a positive difference.