Just to second that Nick, and to give credit where it's absolutely due...

Ratbert got in touch after my post above, and set up ROCK for me on a NUC which I'd bought several months ago, but hadn't yet configured.

Roon has now been running for 5 days straight, not a single drop out or loss of the ID40, every endpoint and remote springs to life immediately, and the whole thing is extremely responsive. A completely different experience from running Roon on an older iMac which was just about wheezing along.

For the first time I'm experiencing Roon as intended, and it's revelatory. And Russ is an absolute Gentleman, giving his time and experience freely (as several of us on the forum have found!) Sincere thanks!

Very Happy Camper!

George