I use the Q701's with the O2 amp and I can say that the O2 can get them quite loud although I can max it out without hitting earsplitting levels.
** Note on this though that my sound card is set to 50% output to avoid clipping from the card which I have seen at higher output levels**
I have never found the treble to be harsh. I think it does have a very nice balanced sound. Bass is nice even on rap/hip hop and electronic music though as others have said I sometimes wish it could dig a bit deeper in the bass department. Also, I personally feel that the revered sound-stage of the Q701 is somewhat overstated. It is a semi-open can and having heard some other truly open ones I do wish it had a bit more air to it. Well, then the bass takes a hit and it's a trade off. You can't have everything I guess.
Awesome thanks for that info. I just placed an order for a White Q701. Hopefully it will impress me... if I feel DAT sound-stage isn't good enough, I will be returning them lol.