Digital audio connection..... Rookie misunderstanding. Hoping for work around.

I purchased a new Gustard x26 pro Dac under the pretense that I could hook up my AVR digital HDMI out to the IIS-HDMI in. I had no idea that IIS is a different protocol and wouldn't work with a regular HDMI cable...uggh. My intent was that I would balance the volume of the DAC and AVR independently. (Honestly Im not sure that would work either.)

So now I'm looking for a work around since I don't have a preamp (the Gustard Dac is directly connected the mono's via XLR), I've spent hours searching the web for different combination of cables and converters to no avail, but I might be looking for something that does't exist due to my lack of understanding of connection protocols among other things. Hopefully someone more knowledgable than myself can help me get the front L&R signal from the AVR to the Gustard to enjoy HT Surround Sound, or at least stop me from "spinning my wheel" searching for the unobtainable.

OK, here the setup:
Streaming though FireTV via HDMI to Denon AVRx3300. (ARC HDMI out to TV)
Denon also has HDMI out for zone 2 (configurable to surround back channel). It's also has RCA pre outs for all channels.
The Gustard has the following in's. AES, USB, IIS-"HDMI", Optical, Coax, and Bluetooth. 
Sony ns900v CD/ SACD player has Optical out, 5 channel RCA out and Coax out.
Node 2i has optical and Coax out (but prefer Coax for hi res streaming).

Does anyone see a way to connect all three to the Gustard ...the Node 2i, Sony NS900v, and the Denon? 

Thanks in advance


Mark