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

Your front 3 speakers should all have the same amp to match as perfectly as possible. If you are using pre-outs to a separate amp use them for all 3 speakers (L-C-R). If you get a 3 channel amp you can use pre-outs for L-C-R. If you can biamp L-R speakers you can get a 5 channel amp which would be stellar and not a lot of money if you go with second hand.

Now, when you have speakers in a second room I would pivot and use a whole house audio system, it gives you more flexibility AND it can be run wireless.
I would connect the ceiling speakers in the second room to a Martin Logan Forte wireless amp (which also has ARC room correction.) It has a streamer built in so you can run it independently of your main system. If you want to have the same music in both room get a Martin Logan Unison preamp/streamer for your main system.
They are on sale at 50% off:

https://www.martinlogan.com/en/category/wireless-systems

@kota1 So something like this: https://www.rotel.com/en-gb/product/rmb-1506

If listening to stereo music meant for 2 channels and not movies, is it ok to have the center speaker connected too? 

Yes, something like that. When you play two channel stereo its fine to have your center channel connected. Your Denon receiver will play back in stereo to just your L-R speakers when selected. What speakers are you using for L-C-R channels?

@kota1  I've got the Fyne Audio 500 home theatre pack. I love Fyne Audio. I've got the 501SP speakers in my dedicated music room. They're great.

So for the home theatre I have:

2x F501 (L+R), 1x F500C (Center), 2x F500 (Surrounds), 1x F3-12 (Sub) and 4x FA500iC (heights).

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. 

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?

Thanks for your advice.

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.