After a few days with my ODAC + o2 I think i'm ready to post.
The very first time I listened I thought I knew what everybody was talking about with this 'Crazy Treble' (I was using K702's) and the treble seemed harsh and very in my face, I then changed USB ports and it sounded fine,although I then put it back into the same USB port as the first time and it again, sounded fine, which confused me a bit.
I discovered that the problem was merely my ears/brain. I first of all hadn't listened to my K702's for a while and secondly had the volume much louder than I usually listen thus giving me this completely different representation of the DAC with super loud treble, although after some listening of familiar tracks I am very very pleased with this DAC.
It really is super-clear, I am re-discovering further elements in tracks that I couldn't quite pick out before (was previously using the headphone out on my Native Instruments Komplete Audio 6 into the o2 Amp) and the instrument seperation is even better than before.
For the money I really couldn't be happier with this DAC, does exactly what it's supposed to, faithfully convert a digital signal into an analog one.
I'm yet to try it with my monitor speakers but if I do soon I'll post it here.
P.S this may be a bit off topic, but when I'm using ableton live with my NI komplete audio 6 it lets me use it under an ASIO driver so it has very low latency, but when I use the ODAC I have to use it as MME/DIRECT X driver type giving annoying latency, anybody know how to fix?