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

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.

@soix

In my setup I use a Sony Signature DAC/pre for my two channel setup while using the exact same speaker/amp configuration for L-C-R channels. When you use an immersive format you need that center to match seemlessly. I agree with using a dedicated pre-amp for stereo but not a different amp.

@kota1 While I agree in principle, in practice I’ve found using the AVR to power the center works well.  To use the same amp across the front would entail buying a separate stereo preamp and a 3-channel amp that will cost A LOT more and add another box and set of interconnects.  To me it’s just not worth all that for the potential benefit, but the OP could certainly do that if he wishes. 

I guess we have had different experience. In a movie the center is the MOST important speaker, to cripple it with the lowest performing amp would not be something I would do. The OP is looking at a 6 channel amp and the Fyne speakers are biampable. The used prices for that amp and are under $1K so it won’t bust the budget. He would have dedicated channels for both low and high frequencies of each speaker (4 channels total) and the F500 channel for the center is also biampable. So, all 6 channels are biamping the front 3 speakers, it will be able to squeeze every bit of performance from those speakers. He also gets the benefits of separates when he adds a dedicated two channel pre with HT bypass in the future, right?