I don't think you will have any issues with sibilance with the M3's as long as you are listening to good recordings.
Exactly. Alan has pointed out that sibilance is present in a number of recordings. If you have a speaker capable of reproducing all the sound on a recording, you will get all
the sound on a recording including compression, clipping, distortion, sibilance.
I have some recordings like those by Yes that are disappointing. I have some extra material on the otherwise decently recorded Thick as a Brick that is painful to listen to.
I also have other recording such as those by Chick Corea, Hiromi Uehara, Dire Straits and others that are pure joy to listen to.
The highs on your M3s will play very cleanly.