My $0.02 as a very happy NV10s owner.
I have little doubt that the NV12 soundboard is superior to the internal speakers on the NV10s in terms of realism and 3D sound. I have Neumann KH310 speakers and have tried to blend the sound via aux in but have mostly given up as I feel that the internal speakers take away from the overall sound quality. I sometimes keep them at a very low setting to provide some vibration to the cabinet but, they are otherwise terrible. The monitors produce fantastic sound, but they're quite directional and I don't find it realistic compared to what comes from an acoustic. Since I typically use headphones it's mostly a non-issue, but it certainly would be nice to have usable internal speakers when I want to fill the room with sound.
I think the NV12 will be great for someone who wants a zero maintenance mini grand for their living room, on full display away from the wall. In my case, the NV10s is exclusively used as a MIDI controller. My unit is covered with sheet music and electronics. The whole thing fits in a small nook, surrounded on three sides. The larger size and piano lid wouldn't work for me. What would be a great would be improved internal speakers and an audio interface. I have a Yamaha P515 in my basement and the audio interface works so much better than the kludgy Kawai audio in for connecting to external monitors.
So congrats to Kawai for continuing to bring their hybrids forward, but IMHO it is not a replacement for the NV10s in the same way that the N3x is not a replacement for the N1x.
BTW- I'm intrigued by the portable external soundboard someone posted. It would be great to see other manufacturers bring this technology forward as I could see supplementing standard monitors with this.
