I use a Sherwood RX4109 to drive my k702s.  It has a warm, vintage tone and drives them very well.  I've tried actual, dedicated headphone amps, but I always find myself going back to this. <0.4% distortion, 98dB SNR, 20hz-100khz frequency response, and a built in equalizer all for less than $100.  A sure buy if you're on a budget.  It gets generally mediocre or bad reviews because the speaker output isn't all that great.  The headphone pre-amp is a separate construction, so it is never, ever included in reviews for this system.  It does have a...