I keep meaning to open a topic on this and I keep telling myself that I'll do it after I have more data. I haven't been listening to music on MC as much recently so haven't had as much opportunity to collect data (anecdotally).
The new options for Audio > Device Settings > Buffering > Software seem to have helped. I've tried 250, 500, 750, and 1000 mS. Each step seems to help more and more. Though the difference between 750 and 1000 is questionable. I estimate that I'm now only getting dropouts every 12 to 15 hours of continuous listening. It's not perfect, but it's sure a lot better than it used to be!
I've backed down to 750 mS of software buffering. I'd really like to go back to 250 or 500 because the delay in pausing is annoying and makes one think that pressing the button didn't work. I've had to program myself to wait after pressing the pause button rather than hitting the button again immediately when the sound doesn't stop. At 1000 mS the effect is really annoying. At 750, less annoying. At 250, it's perfect. Anyway, I'm living with it at 750 mS and it's not a big deal.
App Nap settings don't seem to make a difference, but maybe they do. It's hard to say without rigorous testing and at this point, it takes so much time and effort that I'm over trying to test it any more. Don't take this as a negative. It's just that, for my purposes, I'd rather live with the mild annoyance rather than spend literally a week or more trying to do more testing, spending hours and hours recording my findings in a log.
I'd like to formally thank all of the people that helped on this. I'm not sure who on the JRiver team did most of the work. John maybe? No matter who it was, THANK YOU! I'd like to formally thank Glynor as well. I think your research and ideas lead to making this problem better. I *KNOW* you suggested the bigger software buffers and they definitely help. THANK YOU!
I have a funny feeling this problem will mostly go away by itself as customers buy more modern Macs. I'm somewhat convinced that if I bought an SSD main drive for this machine that ALL of my dropouts would disappear. Glynor has pretty much my exact computer, except his has an SSD drive. He has zero dropouts. I have "some".
Anyway, I'm trying to say, in my long winded way, that this problem is officially closed for me personally.
...and thank you all again.
Brian.