Marantz pm8006 vs Denon PMA-1700NE for combined home theatre and music room

Is your higher priority HT or 2-channel?  If the latter I think you’ll be fine running the center channel from the Denon.  For the stereo amp I’d recommend this Yamaha that’s at a higher level than the ones you listed and can be had at a steep discount here…
https://www.accessories4less.com/make-a-store/item/yamas1200sl-rb/yamaha-a-s1200-stereo-integrated-amplifier-silver/1.html

It has a HT bypass (they call it “Main In”) so when you hook the front L/R preouts from the Denon into the Main In on the Yammy the amp’s volume control is fixed so when playing HT the Denon controls the volume.  Conversely when you choose an input from a stereo source the Denon is completely out of the signal path and only the integrated amp is active.  I used this type of setup for years until I got a dedicated listening room and it really works great.  Hope this helps, and best of luck. 

Id like to have the option for playing the same music in this room to another but perhaps I’m over engineering it. I could just have a Wiim Pro connected to the Denon x3800H and then buy a cheap amp to serve the other room with another Wiim Pro connected to that.

Buy a second Wiim Pro and hook that one up to the Denon for the second zone.

Do you think the Fyne Audio speakers would benefit from a power amp in addition to the Denon or do you think the Denon would suffice for both movies and music?

NO!!!! Absolutely not. You do NOT want to use the Denon for music unless 2-channel is not important, and I think your Fyne speakers deserve better. The beauty of the setup I described above is that the Denon is COMPLETELY out of the signal path for stereo, which is what you want. The amps in the AVR are subpar and its preamp section is even worse and will kill your stereo sound quality. If you care about 2-channel in this system go with the setup I listed above.

@soix thanks! So should I connect the center speaker to the Yamaha as well as per @kota1 suggestion above?

So as per my original message "I was thinking of using the x3800h for my Center Speaker, Surrounds and 4 Height Speakers. I was then thinking of running the fronts via pre-out to another amplifier which has a main-in/HT-bypass to drive the fronts whilst watching movies. If connected via a main-in, it converts the stereo amplifier into a power amp only with the Denon x3800 having full control over volume etc..."

Should I leave the center to be driven by the Denon and keep it out of the signal path for music? If I do this, the F+L will be driven by the Yamaha and the center by the Denon for home theatre.

But all music sources (Wiim Pro, Turntable) will go direct into the Yamaha.

The Fyne speakers are great, you CAN biamp them with 90db sensitivity that rotel should be "fine" to biamp. So:

Denon L-C-R pre outs to Rotel amp. Use a Y connector for L-R channels to biamp.

Denon amp driving the rest of the surrounds.

I would recommend the Martin Logan Forte amp for the speakers in the other room. No need to connect a source like the WIIM, it is also a streamer.

Before adding a dedicated dac/pre for two channel in your HT I would get all of the above sorted out first. Later you can do as Soix suggested, get a dedicated dac/pre amp for your two channel. I run mine that way and it works fine. But it gets confusing if you do everything at once. Get the amp sorted first. I think there are advantages using the rotel for biamping. I would not use different amps for your center, terrible idea. You want a seemless match for your front 3 channels.
This is the amp/streamer I recommend for the other room:

https://www.martinlogan.com/en/product/forte

thanks! So should I connect the center speaker to the Yamaha as well as per @kota1 suggestion above?

No, the Yammy is just a stereo integrated so can only power the front L/R. 
 

So as per my original message "I was thinking of using the x3800h for my Center Speaker, Surrounds and 4 Height Speakers. I was then thinking of running the fronts via pre-out to another amplifier which has a main-in/HT-bypass to drive the fronts whilst watching movies. If connected via a main-in, it converts the stereo amplifier into a power amp only with the Denon x3800 having full control over volume etc..."  Should I leave the center to be driven by the Denon and keep it out of the signal path for music? If I do this, the F+L will be driven by the Yamaha and the center by the Denon for home theatre.  But all music sources (Wiim Pro, Turntable) will go direct into the Yamaha.

Bingo!  You nailed it and that’s exactly what I’d do if I was you FWIW.  It really is a wonderfully elegant and effective setup, and getting the AVR completely out of the signal path for stereo is HUGE.