Hi Mike,
I too had a somewhat similar problem with my system, for which LatencyMon was exceeding its threshold occasionally. Although this didn't cause me a problem in REW, it did cause audible glitches about once or twice a week when listening to music on my system. This caused my listening experience to be completely ruined, as I was always listening for glitches rather that to the music itself. I'm retired with time on my hands, and this experience caused me to launch into a set of experiments that lasted several weeks.
Unlike you, my music playback computer doesn't have a super-powerful CPU - only a low-power two-core AMD Athlon 200GE supporting only 4 concurrent threads. So my problem is likely different from yours, but I'll try to list some software tools I ran into along the way that may help.
In my search, I came across PowerSettingsExplorer as you did, and tried various experiments with it. I was able to get some improvements, but not fix the problem entirely.
Another tool that came in handy was
Driver Store Explorer. This shows a summary of all installed drivers, including both enabled and older, disabled ones. You can see if there's anything suspicious there. Unfortunately, it does not allow you to temporarily disable drivers and enable them later, only delete them. Still, seeing everything at a glance is often useful.
Another useful tool is Autoruns64.exe in the
Sysinternals Suite by Mark Russinovich. He's the guy that originally uncovered the Sony rootkit scandal. Autoruns64 appears to show all items that are loaded at startup, both apps and drivers, when you look at the "Everything" tab. It also shows how they are launched (registry, task scheduler, startup folder, etc.) When run as administrator, it conveniently allows temporarily disabling or re-enabling startup items by simply unchecking or checking the checkbox next to it. I've used this tool to fix may problems.
Also in my travels, I discovered many sites with poor-quality information, including from people and entities that should know better, such as Focusrite. I finally did run into only one high-quality source of information. That was a blog by a guy named Pete Brown, a software engineer at Microsoft who works on the audio subsystem, does customer interface and has his own recording studio. It is called the
Unofficial Windows 10 Audio Workstation build and tweak guide. He provides logical arguments for his suggestions, unlike most sites you'll find out there. It might be worth a look.
In the end, my problem was fixed in an unexpected way. I replaced the USB sound device I was using, an 8-channel Tascam US-16x08, with an 8-channel Topping DM7 DAC. This cut my DPC latency dramatically: about in half. I wasn't expecting this at all, because one of my earlier troubleshooting steps was removing the Tascam and its drivers and trying out a Focusrite 2i2 that I already had. This had the same DPC latency problem as the Tascam. I simply bought the Topping on a lark, not expecting that it would fix my situation. Then, after weeks of listening and zero glitches, I decided to run LatencyMon on it. That's when I discovered the massive DPC latency improvement. I don't know how to explain this. My working hypothesis is that the Topping uses asynchronous USB with a Thesycon driver, and it's possible that async USB usage improves DPC latency somehow. I have no way to prove that though.
Going back to your problem, it might be useful to try the Autoruns64 program to temporarily disable any startup items that look suspicious and see if you get an improvement. The beauty of that tool is that it allows you to put what you've changed back into its original state by just checking a checkbox and rebooting the system.