Are all R2R dacs slow and soft?

No.  The Esoteric XD DACs are R2R, using discrete precision resistors.

My K-01XDSE is certainly "fast", astonishing transients, and its resolution is outstanding - if the last note of a piece is a sustained piano note you can hear when the dampers touch the string(s).

There might be an issues with your HDMI cable.  I Googled asking about using your cable, designed for video, as an I2S cable.

"<>>Bandwidth Paradox: While high-bandwidth cables (like Cinnamon 48) are great for video, their faster signal edges can sometimes create timing issues (brighter/sharper sound) for I2S on certain DACs"

I2S is VERY sensitive to the cable as that cable carries data and clock signals from your Airlens to the DAC.  Your DAC is using the clock signal received over the HDMI cable as its master clock.

If you Google for "Cinnamon 48 cable causing problems on I2S DACs" you will specifically see treble brightness and sibilance as issues, and see suggestions. The consensus seems to be that ultra high bandwidth HDMI cables cause problems with IIS.

Try a cable designed specifically for I2S.

I have ordered the items that audphile1 suggested. 

While you are waiting for those to show up, take those absorbers on the side walls and try them behind your head on the back wall, where you have the diffusers. Or get 2 friends to hold the sofa up 3 feet while you listen. The first option may be easier. 

It looks like they are toed-in quite a bit, crossing in front of the listening postion, but it might be the picture? You have experimented with toe- in I assume? 

Short answer No!

Hope you can figure it out. 

@mclinnguy 
"Perhaps the Audioquest Cinnamon HDMI cable is defective?" I doubt it. Bought it brand new.
"And were these "soft and mushy" other DAC's demoed connected with the same Cinnamon cable?"
No, the other DACs were USB only and I had the OptcalRendu at the time, so this was pre Cinnamon. 
@mechtronic 
I'll try to keep a list as I run into them. 

@danmar123 good question. 
I can answer based on my experience -

when I added that trendnet switch I did it because I wanted to split the output of my router/mesh node into two branches - one that would feed the streaming card in my DAC and one that would feed my Roon Nucleus One. I was hoping that the trendnet will not degrade the sound quality because my older D-Link switch made the sound quality considerably worse. 
What I got with the Trendnet was actually a surprising benefit - quieter background, smoother sonics and improved tone. 
So in OP’s setup, if he hears positive impact from the configuration I recommended he can just get better Ethernet cables and feed both the AirLens and his SGC server a cleaner signal for even more improvement.