I also own the M-100 and am a big fan of them. I actually think the M-100 isolate okay, but Sig DJ may isolate better. I can tell you the Sig DJ has a more solid build with no detectable weak spots like the M-100 wing plates- all plastic is thick and high grade. The Sig DJ blows away M-100 in comfort- cups are much larger, plusher and the most comfortable leather I have felt. Also, the sound signature is similar to the M-100, but the DJ takes the refinement, highs, bass texture to another level. The Sig DJ has replaced the M-100 as my primary headphone and I can't imagine another headphone taking the top spot over the Sig DJ.
Edited by Craigster75 - 2/10/13 at 7:08pm