I'm one of those that is using the Gaia with my Denafrips DAC. I started using it with the Terminator, then upgraded to the Terminator Plus.
In my system, the Gaia made a significant improvement, but this also involved switching from USB to i2S connection to the DAC (USB now goes into the Gaia). Even with the Terminator (with no clock connection between the DAC and DDC) the difference was significant. The improvement in detail, blacker background, sharper imaging was pretty obvious.