The Valhalla does well with Beyers (DT880/990) and some Senns (HD650, never heard this combo but I imagine it'd be too warm for my taste). What's your budget? The Burson HA-160 has a GREAT reputation with the AKG K701/2s (my personal opinion is to not touch the Q701s), K702s with the replaceable cable is cheaper and better than the two. Looks better too (I like black). It will bring out a better bass in the headphones and give them a more full bodied presentation in general while not destroying what the AKGs do best, treble and sound stage. Keep in mind though, they will never be super bassy headphones.