Right - to work:
First thing's first. On the NS1000s in passive mode the difference between a suitable amp and none is the closest thing I've heard to 'night and day' from a single piece of audio equipment. When referring to the NS1000s I'll assume we're using a suitable amp, ANR mode or both. There is none of that sort of difference with the DT770 Pro/250s. The DT770 Pro/250s are not bad without an amp. Certain things improve with one but they don't sound awful without by any means.
Noise floor. E5 has a very slight hiss with the DT770 Pro/250s. Not much really - nothing like as loud as the noise cancelling hiss on NS1000s but it's there. The CMOY isn't silent but it's pretty close at normal listening volume. Hiss is evident when I raise the volume though on both though - more so on the e5.
Loudness - the CMOY drives the headphones a lot louder than the FiiO. With volume set to 50% from my soundcard and mixer I don't want to go above 50% with the CMOY. The e5 is just starting to get uncomfortable on Max volume.
FiiO's bass boost: I'm not really a fan of Bass Boost. The DT770Pro/250s are strong in the bass department anyway and boosting it more is a bit overwhelming. On the NS1000s I think bass boost reduces detail and that's the case here too. For the rest of this - assume I've had bass boost off.
Music testing:
Range of different music here: Motzart, Kurtis Blow, Radiohead, Nick Harper, U2, Newton Faulkner, Gorillaz, Freddie Mercury, Nick Cave and the Bad Seeds, Nitin Sawhney, Frank Sinatra, Delirious?, Jon Gomm, Queen, Van Morrison, BB King, Van Halen, KRS-One, Florence and the Machine, Jeff Buckley, Dizzee Rascal, Alanis Morissette, Everything but the Girl, Ennio Morricone etc etc
At the matched volumes the FiiO sounds compressed compared to the CMOY. The CMOY just seems like it has more power behind it and this is most aparrent in driving the bass. Some of the deep bass sound in Nitin Sawhney's Nadia has real presence on the CMOY compared to the FiiO. The e5 feels like it's failing to capture the dynamics in comparison. The CMOY seems like someone added a sub. Bass can get really low and powerful - but remain clean throughout.
As mentioned before, the mids are a little more recessed than on NS1000. I prefer NS1000s for tracks where vocals dominate - especially female ones. Strings are also another thing the NS1000s do well. The DT770 Pro/250s improve on the NS1000s in ohther areas. Treble performance is similar to the NS1000s with ANR on. It's really the bass where the DT770 Pro/250s shine in comparison. They reach further and are more detailed down there. You hear the bass drum being hit and the double bass plucked. By comparison, the NS1000s have a rather pleasant low-mid bass hump that punches well but doesn't have that much depth.
On both sets of headphones I prefer Dolby Headphone on for pretty much all use except binaural recordings. I did a mix of the above music testing with and without Dolby Headphone but for my own use I would normally use it all the time. The DT770 Pro/250 are a lot less forgiving of the artificial reverb of DH3 than the NS1000s. DH3 is a bit of an echo-chamber fest here. DH1 and DH2 are fine but I have to be more careful about placing the DT770 Pro/250s on my head properly for the effect to do it's job than with the NS1000s. It's probably down to the larger earcups and getting my ears in line with the drivers. Not much room to move around in the NS1000s!
No time to do a detailed gaming roundup just now or use CMSS-3D. Both handle Dolby Headphone well. The NS1000s do this marginally better, giving more depth to the 3d imaging. The DT770 Pro/250s seem to be more like projecting an audio image onto an imaginary surface away from the listener but it is not quite as convincing as with the NS1000s. Still - both are good gaming headphones and the bass of the DT770 Pros can manage a bit more low rumble for explosions etc.
Hmm... Bit later than I'd imagined. Any questions - I'll answer them tomorrow.
Edit: just saw your last FM list. Not a lot I'm familiar with there. I have some Jimi Hendrix Experience stuff and er... Jon Gomm does a Portishead cover in his live sets occasionally...