[Hal Beery] “Please suggest best headphones for this barebones recording situation (sitting in the same room/space as the performance… often tooooo close to the source.)”
To be frank, there aren’t any. Your problem isn’t the headphones, it’s you being in the sound space. No headphone is going to cure that for you.
The problem is that you can’t attenuate more than mid -30s dB with your head in the sound field. The reason for this is that there’s more than one path to a persons eardrums. The main path other then the ear canals themselves are through the sinuses. Which, if you like breathing, are difficult to isolate.
About the best you can do from a headphone perspective is something like the Remote Audio HN-7506, which is a set of Sony MDR-7506 Drivers in a somewhat better closed back isolation case. But I’m telling you up front that these will in no way solve your problem. They will at best improve your situation only marginally.
You’d be better off getting creative. Run some long XLRs and take over a bathroom. Anything with a door. Someone’s office. The lobby (which has it’s own problems, but different ones). Loading dock. Anywhere else but in the room with the musicians.
If you won’t do that, then think about not live mixing. Just get the individual mics down with reasonable levels and mix it in post.
‘Cause there ain’t no magic headphones that will solve this problem. If there were, everyone would have a pair and you wouldn’t need to ask the question in the first place.