Aloha Head-Fiers, I recently picked up a used WA2 on Ebay which came with the stock tubes and upgraded 5998 power tubes. My amp has the preamp section blocked out which is a shame as I would liked to have run it as such. I ran it for a few weeks on the stock tubes and was impressed with its performance with my HD580 and Grado GS1000i. All the reviews I have seen say to use a high impedance cans but the Grados work really well with this amp. They are very detailed with strong clear bass and only the slightest hum on very quiet portions of a track...