Well My MPX3 SLAM Just Died - Replacement? - Page 2

I can't answer that either - except for tubes, mine is stock.  You might want to read this thread, though:

http://www.head-fi.org/forum/thread/402215/the-woo-audio-2

I personally have opted for the Woo WA22 because it uses the same tubes as my Singlepower Extreme.  However, going balanced requires buying at least one balanced cable, which is not a cheap endeavor.  According to Jack Wu the WA22 really requires a balanced source to sound its best, so keep that in mind if your source is single-ended.  If you are still considering the WA22, you have to figure spending at least $200 or more if you buy a balanced cable from Moon Audio, ALO, Whiplash, or A Pure Sound.  

Bottom line: If I was using high impedance headphones like the HD600s (which I am not) I would have gone with the Woo WA2, no questions asked.