i guess the Treble will sound better in case you had a good DAC, sometimes the headphone alone can't shine, unless you pair it with something on the same tier, don't know how good is your E-DAC nor the O2 but i won't let them drive 1k USD headphone. 

Get Beyerdynamic A20 amp and say goodbye to spiky treble on T1. No, seriously.

I have not noticed harsh or sibilant treble on my pair either. I think there is a synergy or quality issue.
Also if you decide you want something more bass/mid centric I would recommend the Audeze range. The HD650/600's are too big a quality drop IMO.

laon, but the frequency response curves also show huge treble spikes so I'm guess the A20 is colouring the real sound of the T1?

nigeljames, I have considered the Audeze range but I think they'd be too heavy and uncomfortable for me, same would be true of the HifiMan range (though the new ones to be released shortly might be interesting).

Shini44, if its to do with the DAC why is everything else except the treble superb?

I agree about the harsh highs. I owned T1 for a while, then sold it. For me, it was too bright.

@Shini44 Ye man , buy an amp / dac that costs 1000$+ and just colors away the flaws of your headphone.