I have an E-800 and it drives both my Sonus Faber Guarneri Homage and Magnepan LRS+ effortlessly. Mucho, mucho headroom. With even more efficient speakers, my goodness, you might be able to reach the volume levels of a stadium rock concert! :)
I’ve not heard the new S version of the amp but cannot imagine how Accuphase was able to improve it in any significantly audible way.