@wynnytsky I have the latest or 12th series Gaia, can't imagine why you'd not find this possible.
So, on Harmony screen, I2S clock setting are you getting message, "no compatible I2S clock available?" When using Gaia clock you should see I2S at top left of display. I can find no evidence earlier Gaia's cannot support choice of using it's internal clock.
I'll reiterate the entire streaming chain needs to be optimized in order to extract full potential of 006. I used to run SOTM usb solution, found the Sonore products superior, specifically the OpticaModule and OpticalRendu, best lps one can afford for these Don't forget the Denafrips DDC also offers further usb opimization via it's STM32F446 Advanced AMR based MCU interface.
@dbb Unfortunate you didn't find the Statement to be your cup of tea.