Yes, the Magni will drive the Q701 with ease. With my ODAC and everything set to 100%, I only need 25% volume on the Magni for my Q701.
I haven't tried the DT-880 600 ohm yet with it, but I have a 600 ohm Sextett. It has ZERO problems with it and has no lack of volume and sounds amazing.
I should point out that the Magni to my ears doesn't add even a touch of warmth. Maybe it does to some, but not to me. At least I can't hear it. I like this though..
Of course you could always use a different source.
I'm sure people have seen my updates, but I do now love the Magni with the Q701. I prefer my Micro Amp for it, but that's much more expensive.
I just know that the Magni is a bit better than the E9 for the Q701.
Seriously, if there's a headphone out there that requires past 90% volume with the Magni and ODAC I wouldn't believe it...maybe the K1000?
Of course if you use a very weak source you'll need to crank the volume up much higher. A docked Ipod for example would need a lot more..