I haven't tried the phones you listed, but I do have the Denon D1100s and with some EQ'ing they can sound pretty darn awesome. What I did was raise the 32 bass while lowering the mid and high bass. I raised the mids and the highers to various degrees and it really opened things up. The D1100's sound very crisp and clear and I'm sure you've heard of the insane bass on this. I have also listened to some Lord of the Rings music and ALL of the songs sounded fantastic. Since you like orchestral music, I can say that the strings sounded good and accurate. They are $135 off amazon at the moment I believe so you should definitely consider it.
Hey just saw this thread. I have my mind set on 2 or 3 models already. I need full-sized, clear sound, with a bit more on the bass side. Mainly for rock and metal, but when I want to listen to Yann Tiersen's violin, it should sound clear and airy. My current equipment is a Sony A845 with the sock IEMs, which to me sound really good. Help is on the way, in the shape of a Fiio E5 and a line-out from Fiio for my Sony.
I was going for the Shure SRH750DJ, but was also considering the Shure SRH840 or the Sennheiser HD448. From what some people wrote, the SRH750s are like the SRH840 but not so neutral, more bass-inclined. However they don't sacrifice mids and treble in order to do so, and like I mentioned, that's important.
Also, my current IEMs are open (I think, because the opening is just for the noise cancelling), and their soundstage sounds ok, I don't have much to compare to. I really enjoy being able to separate the instruments in my head, and blending all together kind of sucks =(
The HD448 have no bass impact, and I'm not sure I want to rely on my Fiio E5 to have that. Same thing with the 840s. They are great headphones, but maybe more for monitoring.
So, now that my extreme requirements have been made knwon, what do you suggest?
PS: The M50s are hard to get where I live, and I have a good deal on the the HD448 and the SRH750