I've been curious about this for while...
What are the highest impedance IEMs on the market at the moment?
There is plenty of voltage at the source to burn so sensitivity is not an issue, just want them to be high impedance so they can be easy on the output stage.
So far I could only find Hifiman Re-262 which is 150 ohms impedance, and maybe Re-0 and 64 ohms... but I'd prefer something in the 300-600 ohms range if such cans exist.
The other option might be to find a pair of sensitive single transducer IEMs with linear impedance across the audio band then heavily pad it down with serial resistance, but I'd prefer to not go that route.
Thanks for your input.