Halcro power amps have a signal ground terminal. I have 4 Esoteric devices and 2 Halcro devices with signal grounds. That is a full set for Altaira. At the moment the Esoteric signal grounds are not connected to anything, and the Halcro signal grounds are connected to the ground terminal of a Denali 6000S/v1. The Altaira will sit next to Everest and be connected to its ground terminal.
If there is a screw-terminal positioned on the back of the chassis that is a designated ground conneection, e.g., as shown on this piece of Esoteric gear, that is usually designated as an earth (aka chassis) ground connection, not a signal ground connection. Also, for most,
but not all gear, if you connect a ohm meter probe from that ground terminal and the ground pin of the IEC receptacle, it will show a connection with a 0 or < 1 ohm reading. An exception to this Constellation gear, and it
may be the same with Esoteric gear, I just don't know as I don't own any Estoteric gear.
Regardless, connect a ground cable from this ground terminal to your Altaira.
The way Esoteric has it labeled is somewhat misleading. In the interests of clarity and accuracy, in the Altaiara guidance documents from Shunyata, when they refer to making a "signal ground" connection, they are referring to an
actual signal cable interface connector, e.g. an RCA or XLR jack, S/PDIF connector, Ethernet RJ45 port, USB A-slot, or BNC port, etc.