So... I've been researching this since I got my Yamamoto. It is supposed to be the best amp ever for the W1000. The best explanation I got so far is that the Yamamoto is very transparent to the source. My source is an Outlaw 970, and that may be it (although I don't find this in using the Outlaw as source for my speakers).
Anyhow, whatever it is, the AD2000 + Yamamoto sound better (in my system, to my ears) than W1000 + Yamamoto.
I'm very happy with the outcome though. :-)