As far as I know, the main

As far as I know, the main thing about impedance is that the higher it is, the lower the sound you will hear. If it was at extremes (pico ohms or less, or giga ohms or greater) than this could be a problem, but standards keep these in the range of something like 32 ohms to 600 ohms I think, which should be fine for anything. I’m not 100% positive about this.

I think what might happen is that the surefire might just sound quieter than what you are ‘supposed’ to have, so you’ll have to ‘learn’ what volume you’ll need to hear to have proper volume recorded.

Don’t quote me on this though! Hopefully someone else will have more of a definite answer.