Maximum Impedance that an iPhone can support?

I am currently looking at the Audio Technica ATH-M50x headset, which has a 38 ohm impedance. I was wondering if anyone has ever tried using an iPhone with high impedance headphones, and had any insight into the playback quality. I will mainly be using these with my laptop, but when I am traveling I would like to use them with my iPhone. If the specific phone makes any difference, I plan to use it with my 6 plus.

I've used 250 Ohm Beyerdynamic DT990s on an iPhone 5 without any issues.

I read that as "maximum independace supported" ...

The maximum independence is obviously 1776.