Hey @Bruce_Elwood – thanks for the detailed report. Makes it much easier for us to help.
If these issues have persisted across two different Core machines, that points to something going on with the network, and since everything seems to be running on wifi (right?) that’s where I would look first.
We’ve had a lot of bad experiences resolved by replacing Airport Extremes, and we generally recommend against them. You can find some good information about resolving that in this post.
I know replacing wifi routers isn’t always the easiest process. If you want to try some other troubleshooting first, I would do what you can to work around the wifi – move the Airport Express closer, move the Naim temporarily and connect it over Ethernet, etc. If things get more stable with wifi out of the picture, at least we’ve localized the problem.
Let @support know how you’re doing and we’ll make sure we get this stable for you Bruce. Thanks!