I'm currently listening to a pair of Grado SR80i's through a MacBook Air but I'm looking to upgrade. I'm currently considering a pair of AKG Q701s (or K701s -- I hear they're the same internally) and a USB DAC/headphone amp. I'm currently considering an Arcam rPac as a DAC/amp but I hear that AKG 701s are hard to drive and require a powerful amp to get the best out of them. Is this true? Will the rPac suffice? I've heard mixed reports about the output of its amplification stage.