WA7 is good, but not that good. It's quite neutral for a tube amp, very detailed and well extended - at least with the upgraded tubes and power supply. The sound is subtle and comes from a noise free background. What it lacks for me though is pure raw brutal slam. It just doesn't deliver in this department.
I have been using it with the HD800 for about a year, but if you disregard the honeymoon period, I have been most of that time on the outlook for something more satisfying, as it always had me wanting more and feeling there must be another level out there. And there is.
I don't want to sway you to spend more, as that may be necessary to get to that level, but rather set your expectations right. With the WA7 you'd be getting a very capable and quite enjoyable amp that can handle most of dynamic and planar headphones, but if my experience is any indication, it won't deliver the end-game feeling.