@aberyclark few things to consider…
1. mac is decent as Roon core assuming it’s up to spec of what Roon recommends
2. Roon is very demanding when it comes to resource consumption. Using one machine as roon core and streamer is not the best approach.
I have tested my Mac Mini 2018 (Roon core) as a streamer against AURALiC Aries G1 and my current streamer, Lumin U1 Mini. In both cases the Mac Mini was beat. Some of the improvements I noticed were less “digital”, less midrange glare and more relaxed, natural sound. Also lower noise floor, better imaging and soundstage.
I’m not familiar with iFi Zen streamer or the Pro-Ject. But I can highly recommend Lumin.