I'm glad to hear that you found an amp that you're enjoying more. I did want to ask if you're volume matching between the 2 amps. For a-b testing, anything that plays louder tends to sound a lot better, at least initially. The louder amp will always sound more dynamic, more open, and livelier. If you went to a store and compared Quads to Klipschorns with the same amp at the same setting, your first impression would be that the Klipschorns had more detail, were more fun to listen to. This would especially be true if you're listening to 9 Inch Nails. fwiw, I suspect many people who listen to 9 Inch Nails want more absolute volume and a sense of the beat.
I suspect a 10" full range speaker, even a very efficient one, might not be the best match for what the Volt+ does well, especially if you're looking to rock out (you're still trying to control a pretty big magnet). Given your taste in music and choice of speakers, I'm pretty sure you're making the right choice with the nuforce. For your preferences, even with your very efficient speakers, I think class a/b is the way to go unless you can afford high power true class A.
My take is that the Volt+ is really more for folks who like SETs. They have bass, but I've never thought they do "Slam" very well. They also tend to be most magical in the midrange. I also don't think that's where a 10" full range is going to excel, though I'm sure the people at Zu will disagree with me. It's also the reason I listen to more rock and full orchestra when I switch from the Volt+D to the TPA 3255. and more chamber music, folk, and small group jazz with the Volt+D.