Just thought this experience might be worth sharing.
I discovered Roon earlier this year, bought a lifetime licence and ever since have been having fun working out how best to set it up with the kit I already have. Recently I started to get the “Unable to play the station…” message while playing internet radio. This happened sporadically, sometimes after a few minutes, sometimes hours. I also noticed that it would stop mid track when playing local music.
I experimented and discovered that it got worse the more systems I added to a group. 1 would work for quite some time, 3 would fall over frequently.
I have 4 main sound systems in different rooms, all use some sort of Apple mac computer as the Audio Device Driver (Endpoint); a mac pro, an iMac and 2 mac mini’s. The Roon Core is running on one of the mac minis.
Activity Monitor let me see how hard each of the macs was working. I discovered that the mac mini with the Roon Core was frequently running flat out. The mac pro, iMac and the other mac mini were just ticking over.
The Roon Core mac turned out to be a 2009 Macmini 3.1 with 2.26 GHz Intel Core 2 Duo and 4GB RAM, the most it can take. I’d used this because it has a built in Optical drive. I checked the other Mac mini and it is a Mid 2011 with a 2.3 Ghz Dual-Core Intel Core i5 and 8 GB RAM, basically a much more capable machine.
I moved the Roon Core to this higher spec mac mini and the problems have gone away. It has now been running internet radio for over 25 hours without dropping out 
Conclusion - the 2009 Mac mini is not up to the task of running a Roon Core but it is OK for use as an Audio Device driver (Endpoint).
Yes, I would say, any computer that can run RoonBridge can be used as an endpoint efficiently since in Roon Endpoints don’t do a lot of processing at all. Some users by those 130 USD all in one PCs just to run RoonBridge and the drivers for their DSD DACs, for example. As slow as they are, they work great as an endpoint.
Yes, that’s effectively what I’m doing with the old 2009 Mac mini. It’s got a Douk Audio usb to S/PDIF adapter feeding into a Shiit Bifrost DAC.