To your first point, you are correct. I have high hopes for the NAD HP50 coming out in September in the under $300 category.
To your cost comparison between the Sig DJ and M-100, I spent just over 2X as much for the Sig DJ, so it sounds like you found a great deal on the M-100 and I found a great deal on the Sig DJ.
Woah! Wait! You found Sig DJs for $200? If I find them at that price I'm pulling the trigger no matter what. And I too am looking forward to the NAD HP50. Hopefully I can get my hands on a pair.