Very interesting thread indeed ...
(my music preferences: Jazz, Vocals, Classical, Acoustic, Audiophile, Indian etc. ... hardly any rock, no metal etc.)
AKG-701 - They need to be re-cabled and burnt in for at least 300 hours to really reward you with reference quality sound ... stock 701's are lifeless ... yes I have compared them with AKG 1000 in Woo Audio 5 amp with WE 300 tubes with a couple of audio buddies - both of them slightly preferred the re-cabled701 over AKG-1000 - and I could understand that - though 1000 were amazing by themselves - a classic ...
Same with Senn 600 - they need to be re-cabled AND need a matching good quality powered amp - otherwise they sound ho-hum ... (they can benefit from removal of foam (and / or grill) to open them up ...
M50s are quite good for their price - I found them very easy to listen to - amped or straight out of ipod - they were portable and constructed very well - all for ~$100 - what's not to like about them at that price - I eventually got 840s - they sounded even better and now 940 - though better than previous two, do not sound as balanced and the other two - perhaps more burn-in will help ...
For me, the most over-rated were the Ultrasone 2500, I even had Ed 8 for a week for a review - I respectfully returned them - I found them very colored and bloated ... I bet they sound fantastic to some people in their system based on their system preferences.
I Like the HiFiMan offerings - I had their HE-5 - really liked them - better than recabled AKG701 in most areas ... but not their treble ...
I am beginning to think that we have different ears and possibly our ears are "EQ-ed" differently and each one of us are sensitive to certain frequencies more than others ... what is dull for one may be smooth for someone else - what is detailed for one is bright for another etc ...
Yes, I do believe that there can be a reference or several references for that matter and we may deviate from that - based on music type (genre, compression), equipment (source, amp, cables) and preferences (flat, fun, colored, EQ etc.)
This only goes to show the importance of trying a headphone in your system ... to really make a proper opinion of them for yourself ...
Cheers
Sunil.