Hi there !
I had NAF 845SE and, since almost a year I have NAF: Stereo 845SE + pre Amati.
These amplifiers are great.
Stock tubes are ok, but do not show NAF's full potential.
You have 4 pair of tubes there.
Each type meters and only one stock type was the "end game". Raytheons 5687.
I changed tubes making some extended comparisons before, and of course listened to my tube-friends.
As for the 3D sound.
NAF is not an issue here. It can reproduce spectacular 3D image.
My experience led me to the point it is all about acoustics.
My advice is to try with different speakers angle. That was the case in my system with conventional speakers. Take a look at my place and the final angle ! In my room the scene is reproduced not only between speakers as it appears natural in this position no, the scene is also way on the side of the left and right speaker.
For me the best way to adjust 3D image was to use some live performance where the audience cheers. If you can hear in each place in front of you there is the audience clapping their hands, it's ok. I found it goes along with better piano tone and the feeling of depth.
If you hear audience mostly on both sides - it's not ok.
Just my experience.