Listened to NIN Into the Void, cranked it up to about 85db. Big powerful sound, filled the room, lots of information to dissect (the Sim and Sopra's were easily up to the task). With all the soundstaging in the mix, IMHO the main vocals are purposely more focused as opposed to swimming around, they sound centered, big and forceful coming in at 1:23 at 2:27 they get even bigger in the mix. The drums at 47 seconds are chest pounding. I am about 15 feet from the speakers and the main vocals are very big. Love the pull dynamics/back at 3:23, I was not familiar with this track, it is very good for demo purposes. The last minute is when the Sopra's really start to flex their muscles, the bottom is killer, the main vocals are blending with the backups and everything keeps getting bigger. The last "Tired to save my self..." Vocals only is huge.Very cool.
Not sure what was the issue with your demo, this is a wow song for demo and it wowed me. Perhaps it was your front end. I can only comment on the Sopra's with my integrateds, Simaudio and Hegel love the Sopras.
Hope this helps.