So I A/B compared my DT880 with an Sennheiser HD600, Sennheiser HD650 and AKG 712 Pro today.
AKG 712 Pro
Moderately bigger sound stage, mids were sloppy bass response seemed slow, had a mildly warmer base, treble seemed all over the place. Resolution felt bloated. Really quite disappointed considering the hype I had perceived.
Best asped - Very comfortable.
Sennheiser HD600
First thing I noticed was the clamp, wow but I got use to it.Imagine was incredibly accurate, better than the 880s however the treble was definitely rolled off and was missing some of the higher details in the songs I listened to. The insane thing to me is how narrow the sound stage was, it felt incredibly constrained.
Best aspect - strong mids, nice headband padding.
Sennheiser HD650
Bigger sound stage than the HD600, still not as big as the 880s. Mid clarity was lower than the HD600 and even less the 880s surprisingly. Less comfortable to wear. Warmer sound but it really felt like music was being lost in the high end for a mild, almost unnoticeable increase in warmth compared to the 880s, not even sure I can pin it down. The 880s have better soundstage, resolution and imaging than this headphone. The differences are very mild but the obvious loss is in the high end. Detail is sacrificed in the highs, mids have lost resolution for a mild improvement in soundstage.
Best aspect - comfortable to listen to, moderate to average mids.
Honestly owning the DT 880s I felt there was no reason to get any one of these 3 headphones. I rejected the HD600 based on the narrow sound stage, it felt more compressed than my IEMs in a few songs and already have access to this level (actually more) neutrality with improved soundstage with my Etymotic ER4P. The AKG was rejected due to just having poor clarity / resolution in the mids and slightly recessed almost treble. The HD650 is the closest thing to the 880s but is really not competent when A/B'ed for treble, there was chunks of music just missing.
Store clerk said I would ruin my day if I listened to the Beyerdynamic DT1990.
Beyerdynamic DT1990
Holy $hit. I can't even explain the difference. The soundstage was just as big as the AKG 712 Pro, it felt bigger, the imaging was the level of the HD600 across the large sound stage, with better resolution, the bass wiped the floor with the other 3 headphones. The build quality was amazing and it was like I could hear 1.5 to 2x the depth of every song I played. This headset is insane. I think I'm just going to save up and buy these.
Beyerdynamic DT1770
Tried these because the store clerk just wanted to mess with me. Isolation was great, it almost felt as if I had all noise blocked as soon as I wore these, same build quality as the 1990. Once again better soundstage (somehow) than everything but the DT1990, trebles weren't dampened as I thought they might have been imaging was still there. Bass had maybe too much rumble for me. Bass heavy tracks were enjoyable but any poor bass recording was completely exposed.
I just had my day ruined, there was no way I was going to get anything but the DT1990 or the DT1770, however I need to save up a bit more money as these make all other headphones in the store seem incompetent.
Also at the end of the day, there is no need to buy anything from AKG and Sennheiser if you have the DT880s, in the same price range or even $200+ more expensive. The DT880s are a complete steal for the price that they are currently being sold at and to my ears beat the competition heartily.