need amp recommendations for more separation of instruments

I have no way to know how your setup sounds compared to mine, but we have a few things in common. 
 

My setup is a Pathos Classic One Mkiii (similar price point to your NAD) and I have Focal 836v speakers. I also had the opportunity to audition my speakers on the Krell mono block gear that intended for the Focal Grande Utopia speakers. You could say that I “heard things” that I’ve never heard since. I actually selected the 836v over the 816v primary based on the sound of a harp in a Josh Groban song. 
 

I recently upgraded my source to a Denafrips Ares II and them moved to a Morrow Audio MA4 balanced interconnect and the combination of the two really improved the instrument separation for me.  My setup is far from optimized due to the physical limitations of a relatively small house, but I would consider a better source (depending on what you have) as a potential place to make a big improvement. 

It is mostly a matter of the detail in the music getting lost when a lot of things are happening at the same time.  Is placement going to help with that?

Yes.  And it’s free!  Again I ask, how far are your speakers out from the back wall?

@soix exactly right on all counts.

@ahuvia old mate from work had us over. I asked how he liked the speakers, and he mentioned they we better in the shop.
I asked if I could move them and pulled them out from the wall about 1/2 meter. (20” or maybe more).

Liking the sound, he said, ”How does the work?”.
I said, “like PF magik… Now just mark the floor with masking tape and move em around from here… It might get better.”

Of course he just left em there, but it really opened things up.

If we knew your room size it might help…

Mine speakers are about 3’ to a meter off the wall at one house.
The other place has more WAF constraints, and I may also need to change speakers..

Review and test of FDA TECHNICS SU-C700 EG-S amplifier

One of the best, if not the best amp I listened to since 30 years, what ever the price !

Four years ago, after acquiring Atma Sphere M-60 amplifiers for my Quad 2912 speakers I have posted the following comment on audioreview site.

"After various solid state and tubes amplifiers (including all Quads, several Jadis and McIntosh etc) M60 amplification is a huge improvement in my system ! My overall impression is: everything sounds MUCH more realistic, there are MUCH more details, there’s no coloration of any kind, voices are so natural, every single sound can be perceived. You can actually mentally concentrate your attention on each instrument or just listen the whole scene in an organic way. In a sense, you can ”see” music both in microscopic details and as a whole picture at the same time. So, the first impression on listening OTL amplifiers is surprising. The sound is different compared to "classic" tube amplifiers, but it is also different compared to solid-state amplifiers. You may need a few minutes to adapt your ears to this new level of perception. M-60 MK 3 reunite the richness of details carracterristic for solid state amplification, and musicality characteristic for tube sound."

I still stand behind those words as M-60 provides exceptionnal instrument separation. Particularly on electrostatic speakers. Recently Atma Sphere has came up with Class D amplfier that sounds surprisingly simmilar to M-60.

So if anyone is looking for better instrument separation, a greater transparancy, more details... I highly recommend to test these exceptionnal Made in USA products. I’m french, we have many fine amplifiers here, but I still have to find any amplifier in any budget that sounds better.

Also, do not neglect the importance of better source. Room treatement may help a lot, but essentialy better electronics are critical for better sound, in my humble opinion.