I've had the UE9000's which were similar to the UE6000. The main problem i found with them is their headband. There is very little padding which i find uncomfortable for wearing over long period of time. While the ue6000's are lighter than the ue9000's it may mean that there will be less pressure on the top of your head than the 9k's. Sound quaility wise, they are alright. I found with the noice cancelling on the bass is overpowering and drown out the mids. They are nice looking though. I did get to comepare the UE9000's (Same drivers as the 6k's i think) to my ATH-M50's and i will say the sound on the M50s were more pleasent. I done like the highs too much on the M50's, i would prefer something warmer. Portability wise the M50's are soso, being left with a 3m long cable and a thick jack makes it hard to plug into my device. I've started to coil to cable up in loops and stick it in my pocket which more or less solves the problem but i would of prefered a detachable cable. The M50's feel great around your neck, the fact that the earpads fold lessens the bulkiness of the cans. IMO i think the M50's look nice. I cant speak for the M80's but they seem like a bassheads headphones. If i were to pick one i would choose the M50's if you can manage the annoyingly long cable for portable use, i think i have a soft spot for these cans since they were my entry into the audiophile market.
Btw, you just missed a black friday deal on the UE6000's where you could get them as cheap as $15 :( I got the UE9000's for $140 during that same deal.
Edited by Martinrm - 12/23/13 at 7:30am