Hmmmm - interesting. I read it. Pleased they work for you, but as an ex owner of both (so I had quite a bit of time with both), here's what I think .....
This was the first bit that set off alarm bells. You've "thoroughly" tested the SRH 940 for one day - and they're better than the DT880 - OK .....
Suggest you google SRH940 and "broken headband". It's one of the poorest builds Shure ever put together and has a history of breaking - even if you take immaculate care of them. As far as long term comfort goes - those bumps on the headband also got annoying after a while for me. As far as comfort and build goes - the DT880 are miles ahead. Guarantee the majority will think the same.
Bass is OK - I'd argue that the DT880 is far more linear with better sub-bass. SRH940 also has a notch between mid and sub bass that's hard to pick up at first - but over time you may find it annoying. It's one of the things that led to me selling my pair. The bass on the 940's is fast anyway - but I doubt there would be more bass than the DT880. Did you level match when you were making your comparison?
Mids - yep they are warm and dry, slightly euphonic, very forward and
very coloured, and not in the slightest what I would call "realistic".
Treble accurate - um, not really. Let's agree to disagree on that one.
The DT880 isn't mid-range recessed, it's actually pretty flat - one of the more neutral headphones I've heard. the difference is that the SRH940 is quite mid-forward. Easy to listen to the 940 though and draw the wrong conclusion.
Again though - with your A/B comparison - did you volume match the two headphones, and how?
Yeah - nah! I'd ask again about the volume matching - but it's pretty obvious you didn't. Don't worry - it's an easy mistake to make. What is louder to us sounds better - it's the way we are wired. As far as the 940 benefiting from an amp - it's a headphone with 42 ohm impedance and a sensitivity of 100 dB mW IE it's designed to sound really good out of even a smartphone. IMO it didn't benefit from amping - and what you're describing doesn't gel with the actual specifications or my own experience.
Agree with you on the sound stage - the SRH940 isn't too bad for a closed can. The DT880 is far better with both imaging and staging though. Also agree with your comments on lack of bass, and too forward mid-range with the SRH940.
Hey I'm pleased the 940's tick your boxes - enjoy them. Just beware about making a lot of claims about the cans (especially in a DT880 appreciation thread!), when you've had them less than a day, and don't really know them that well. Come back in 4-6 weeks wehn you've grown used to their signature and can give a balanced comparison between the two (without the new toy syndrome hype) - and I'm sure you'll get some interest in what you have to report.
This is the bit that made me smile the most. You haven't heard the SRH1840 or SRH1440, yet you already appear to know their signature and imaging ability (which you've got totally wrong by the way), and are ready to recommend the SRH940 regardless .......
I owned the SRH1840 as well - similar tonality to an HD600 in many ways - just without the mid-bass hump. Very, very neutral. Not an expansive stage, but magical imaging. Far better bass quality than the SRH940, and far more comfortable. I've seen them occasionally for as low as $350 second hand, and I would have rebought it again if I didn't have my HD600 and T1.
Anyway - I digress. Sorry if it sounds as though I'm picking your post to pieces - I guess I am, but not trying to attack you personally. I'd suggest taking some time to get to know your headphones first, and see if you can volume match with an spl meter (smartphone and app with standard test tones can get you to within 1dB), when making comparisons.
Enjoy the SRH940 - they are definitely euphoric sounding when you first get them. For me personally, that wore off in a few weeks, and I got to realise they were a bit too coloured for my personal tastes. The DT880 though - pure magic. I'd still have mine if I hadn't switched to the T1. And that's a whole different ball game