Honesty, it was years ago at a meet that I had the opportunity to compare my WA3 to someone else's WA6, side-by-side. I recall preferring the WA3, but I can't remember what the sound differences were. Sorry. FWIW, I also did the same at that meet (and another one, a year later) with a BHC + Speedball, and had a similar reaction. So did the owner of the BHC; he asked if he could borrow a power tube (a Tung-Sol 5998, IIRC) and was impressed by the difference in sound. The WA3 is an under appreciated amp on Head-Fi. EDIT: ... with the HD-650, IMO.