If you need to use headphone for long session. I think ATH-R70x might meet your expectation. Sound quite flat and detailed, very comfortable to wear for very long session. I favor to use r70x to listen very long concert (3-4hours). but I'm not sure about 8 hours. Only one minus, it quite power hungry. It have 470ohm impedance but 99db sensitivity. Someone said it able to use with portable because it very sensitive. But I suggest to use with headphone amp that have high power (I used with stack D50s+A50s) because even if you able to hear from low power source but sound will be very dull and less detail. I think current price dropped to around 250USD(from 349USD).
I have many Audio technica headphones such as m40x,msr7,msr7b,sr9,ap2000ti. But I give the best all rounder for r70x.It very detailed(to hear small detail in the concert record clearer such as fan chant calling or clapping) and tonal well balanced not treble peak like msr7/msr7b.
I have many Audio technica headphones such as m40x,msr7,msr7b,sr9,ap2000ti. But I give the best all rounder for r70x.It very detailed(to hear small detail in the concert record clearer such as fan chant calling or clapping) and tonal well balanced not treble peak like msr7/msr7b.