Is my HDMI audio out really an i2s connection?

That HDMI marked "audio" may be for a hi-rez audio signal from a streaming source. That player appears to be capable of streaming!

The X1100ES also has left and right audio RCA's. Why not try them instead of your DAC? Have someone make the switch into your amp so you don't have sighted bias. Listen over a few days. The result might surprise you!

No.  To get an i2S signal you’ll need to get a DDC like a Singxer SU-6, Musician Pisces, Denafrips Iris, etc. and run the digital out from your Sony into that. 

Thank you jasonbourne71and soix. My plan was to run a signal from my Bu-Ray transport to my Gustard A26 then then analog out to my ARC integrated. I was wondering if the HDMI Audio Out on the Sony was in fact a i2s connection. Yes, I could use the RCA out to my integrated but then I get less than desirable clocking and processing that my Gustard can otherwise provide. I was just exploring a way to use my Sony unit as a transport and my Gustard as the DAC. I could go the with the toslink optical output on my my Sony to the Gustard. I will likely try that. Again, thank you for your input.

No and furthermore no.