I have a very different perspective, not being based in North America!
First, when I play SACD I use more than 2 channels. The European way of sending digital audio uses purpose designed HDMI technology which supports a huge array of formats and channels. HDMI includes Ethernet, almost as an afterthought!
On the other hand, I2S was designed in 1957 to allow two integrated circuits on a board to communicate 2-channel 16-bit PCM encoded audio. To communicate between boards, I2S developers have borrowed the HDMI connectors and cable, but not the rest of the technology. Why anyone would throw away most of the channels recorded on a SACD is beyond me.
I have a couple of universal disk transports which play SACD along with 4k Blu-Ray, DVD and CDs. These transports output via two HDMI cables, one exclusively for audio. In this mode, they obviously rely on an external DAC.
One of my transports is an ultracheap Sony - about $250 - and it is only a transport. My other unit is a Reavon for about 10 times the price. Amazingly, it contains two Burr-Brown DACs but they are a complete waste for SACD. SACD is down converted to CD quality - something I found immediately noticeable. As a transport outputting HDMI, the Reavon is fine.
Some of the Dolby Atmos multi-channel recordings, delivered on Blu-Ray Audio-only disks, are absolutely stunning. I am mainly referencing the Norwegian www.2L.no label. These disks play natively on each of my transports.
