I am still not convinced that any of the streamers mentioned or recommended in this thread, other than the Node, have the VARIABLE DIGITALOUTPUT (not screaming just emphasizing) required by the GAN1. None of the documentation explicitly states that they do.
The majority of DACs and streamer/DACs, including the afore-mentioned streamers, utilize digital attenuation for volume control. This allows users to adjust volume and transmit scaled-down signal samples to external DACs through various digital outputs (usb, Toslink, coaxial, etc.) and analog outputs (SE or XLR). Additionally, users can switch to a fixed volume control mode to bypass altering the signal when sending it to an external DAC.
Now, there is on-going debate about the degraded quality of the scaled down signal samples through digital attenuation due to the lowered dynamic range (DR) and signal-to-noise ratio (SNR) at higher levels of attenuation. To that end, some manufactures, like RME, claim "In reality, current circuitry overturns the theory, and the SNR at the output of such a device (referred to an analog volume attenuator) is no better than a digitally controlled one" Gustard R26 / A26 also uses digital volume control but supplements a feature that, when turned on, utilizes analog attenuator to mitigate the dynamic performance loss at low listening level. As a result, digital volume control is not considered a significant drawback, especially in higher-end products.