As posted above, it sounded like listening through boiling oil. McIntosh amp.
I tried some of my “not favorite songs” fatigue evaluation test tracks. Worst case scenarios. I intentionally include noise/experimental (e.g., Sleigh Bells) and things that cause me fatigue on almost every system ever tried (e.g., My Bloody Valentine). Some of these tracks have proven to sound drastically different across random headphones/speakers too (e.g., Steve Aoki).
I’d accept that some setups and content could set the ribbon drivers fluttering and thereby make them muddy. Or, the McIntosh amp was not suitable.