Amp/Preamps vs. High end AV Receivers

Thanks for all your responses and let me add more details to get more intelligent inputs.

AV Receiver - Onkyo TX NR809 (Model from 2012) (HDMI, but no 4K)
5.1 Setup
Bowers & Wilkins Speakers and Sub.
Front: B&W CM8
Center: B&W HTM62
Rears: B&W CM5
Sub: ASW610

I watch movies and listen to music + music videos (frequently).
Looking to upgrade to Dolby Atmos Setup 5.1.2. Have not decided on the speakers for .2. My current receiver does not support it.

Hope this helps to give more solid inputs.

Well, I’m still using my TX-NR809 in my bedroom system. The thing is a 40 pound beast, and I’m not sure you can get much better audio quality with any of these newer AVRs.

And 4K capability is not really required in an AVR if you get a UHD Blu-ray player that has dual HDMI outputs, one for video and one for audio. You connect the audio one to your AVR and the video one to your 4K TV. This is what I’m currently doing with my Denon AVR-X5200 and Oppo UDP-203 in the family room system.

I’m also using a separate power amp for the front L/R channels in both the bedroom and family room systems.

Edit:  I see you added that you want to go to Dolby Atmos.  That WOULD require a new AVR or Pre-pro. 

when I replaced the front channels on my Onkyo AVR with a same power Parasound amp, I was quite surprised at the huge difference in sound quality, both for music and movies...

For your speaker surround system you don't really need AV separates cause they will cost you more. Just get a very good and very competent av receiver.
Get the Rotel RAP-1580 av receiver for your B&W speaker surround system. The Rotel will pair really well with the B&W. The RAP-1580 is Rotel’s only AV receiver model and it currently retails for $3800. It is a great sounding receiver and its stereo performance for music playbacks is pretty good especially coming from an AV receiver.

Or at cheaper price point I highly recommend the Cambridge Audio CRX200 av receiver currently retails for $2k. It’s pretty musical sounding av receiver. It will sound good on your B&W.

Integrated Amplifiers are another story ,seperate almost allways are better 
do to separation of RF, and noise , and bigger power supplies and capacitance .
that being said .my brother has the latest Gryphon Diablo ,and it is almost 85 lbs 
and Everything Premium ,and I am into system modding it is a work of art 
and will compete with ease Any seperates in the $20k plus range .
an integrated can have advantages if properly implemented such as no extra cables ,losses in signal there direct wiring and coupled  can have its own synergy 
with amp preamp in one package .$17k is not cheap and their $4k digital module 
is Excellent . If he ever sells it .i will take it Off his hands . I have the Very good Danish Gato 400-S Digital integrated amp that I feel a true bargain at $6500
i  have spent a homes worth on Audio overthe years and owned a audio store 
in The U.K . I feel well implemented class A,AB, Digital ,and Vacuum Tube 
all have examples that are excellent . To date the Gryphon  integrated 
is the most musical integrated I have heard. Vitus  from Denmark another Great equally as good
hand built integrated, their top seperates are better stil  if youhave $40k and up 
I donot .  A McIntosh receiver is very respectable , Accuphase much better still.
we are speaking of High quality gear. Denon, onykyo is ok for a starter system 
Audiophile quality they are not.