They share the drivers, so tecnicaly they are in theory capable of delivering the same sound, the difference lies in the cups and headbands, the headband is pure comfort and look, the cups are very different one closed and one is open..
so signature wise the difference is that the pro80 is more intimate, has a smaller stage, more kick in the bass, and less treble, the isolation also gives a feeling of a more detailed sound, but that is an illusion a powerfull one, but the details are there in the 2050, you just need a more silent place to sit to hear them..
the 2050 has a more open tonality (big surprice) bigger stage, a bit sharper bass, and also has a more lively sound..
I prefer the pro80, but not by a big margin, it is just more pratical with a closed phone, so that my wife does not send me to Gulag or something worse.
It is also a question of the music you prefer, if you like classic music the 2050 is the correct choice, if I knew anything or listened to Jazz it would also be my choice also for the real hevay guys in rock I would prefer the open phone especially if we are talking the fast type..
For classic rock, pop, tecno, pop and most popular music in general I would grab the pro80..
We are not talking huge differenences here, more subtle nuances..
Compared to the HD681 (out of memory) both will deliver a much more comfortable treble, the 681 could be a bit piercing in that area, you will get much firmer and less bloated bass, the mids are a bit more forward in the 2050, in the pro80 it almost takes up the same place and space just better compared to HD681..
If you like the WOWeffect from HD681 the pro80 would be the better choice, the 2050 is more neutral/natural in sound..
It is a great thing to have both LOL
If you could tell me what you think is the weak/strong spots in the HD681, I would get a better picture..
We all hear stuff different and without common ground it is a bit tricky..
My feelings about the HD681 is that it is a phone which makes you say WOW this is great, when you put them on for the first time, but gets a bit boring in the long run, for the same reasons..
Also the size of your ears might come into play, if you got BIG ears the pro80 is not the most comfortable one, also the pro80 gets warmer, it will not boil you brain like HD681 does, but the 2050 is a better ventilated phone and does not get as hot on the ears as the pro80..