The Midi Spec for GLD is here: https://www.allen-heath.com/media/GLD-MIDI-and-TCPIP-Protocol-V1.4_2.pdf
The Following can be controlled by MIDI:
• Fader levels
• Mutes
• Send levels
• DCA assign
• Input to Main assign • Preamp – Gain
• Preamp – Pad, 48V • Name & Colour
• Scene Recall
• MIDI transport
• Mix Select
Some of the above are useful – especially Mutes, Scene recalls, and Mix Select which could be directly controlled by midi but you can’t control the softkeys directly. As you can remotely recall scenes- and scenes can be customised to contain whatever you want including custom softkey settings you might want to take a look at my video of an iPod touch with TCPIP app controlling softkeys on an iLive (should also work on GLD?). See here: https://www.youtube.com/watch?v=1kaPNjQz5pY
Cheers