Just a quick interim report:
Context: Gaia connected to Terminator Plus via i2s via both HDMI and Ethernet (RJ45), with the clock out feature of the Terminator Plus engaged. Speaker setup used for the evaluation.
Ethernet: Alternating between the Sablon 2020 Panatela Ethernet and prior model Sablon Panatela Ethernet.
HDMI: Tubulus Argentus
Both the ethernet and HDMI cables are attached, so I can quickly switch between ethernet input and HDMI input with the click of the input button on the Terminator Plus while the song is playing, allowing for easy A/B testing.
Song: I am listening to all my usual demo tracks but in particular this evening I am using "In Strange Company He Spoke Softly" by MATstudio. This is a great song for demo purposes as it is fairly sparse music with incredible amounts of hyper detail and sound staging elements. It makes it easy to focus on individual sonic aspects. I like this music, it may not be your cup of tea, but nonetheless, the song is a great evaluation tool.
When I am using HDMI, it is i2s via LVDS, and when ethernet is used it is i2s via LVCMOS. I understand LVDS is viewed by some as a technically "on paper" better solution.
HDMI: As compared to ethernet connections, the sound is relatively more dense, a bit more organic- it emphasizes tone and timbre. There is more presence on vocal tracks. It imposes a layer of "beautification" and is very pleasing.
RJ45 Ethernet: As compared to the HDMI connection, the ethernet connection has more clarity and superior precision with instrumental layering, and more crispy and speedy transients. The very subtle musical details are more apparent. Ethernet here is comparatively less "organic" sounding. It is more raw sounding, without the "beautification" of the HDMI connection. I am finding I prefer this connection method, but could very easily live with and be happy with HDMI.
The comments above are just relative to each other. So for example, the HDMI is very transparent and clear, just less so than the Ethernet, and Ethernet is also organic sounding, just less so than HDMI.
The sonic differences above are most certainly a result of multiple factors, namely, the cables used, the Gaia and Terminator Plus themselves, and probably LVDS vs. LVCMOS.
The differences are not at all subtle and the very easy and quick A/B with just the push of the button allowed the differences to really jump out. I could see people strongly preferring one over the other based upon personal preferences, music and equipment. I was very surprised the differences were so noticeable.
Having had this experience, I am now thinking that having multiple output options of the Gaia is a terrific thing particularly if someone has a DAC with lots of connection options, as each connection type differs in sound.
P.S. Forgot to mention- I am far enough into my evaluation process to definitively state that Gaia+Terminator Plus is unquestionably superior to usb straight in to Terminator Plus (no Gaia).