curtsiUnfortunatelly there isn't general answer, there are different opinions, a lot depends on the circumstances and on what kind of sound you like. And to top it all, in spite of that the Q701 is not a high impedance headphone, they say it is hard to drive properly... Take a look around on forums (e.g. http://www.head-fi.org/t/473358/tube-amp-with-low-impedance-headphones)