gain can’t be ganged.
Other solution is to use channel 45-46 and/or 47-48 as they are stereo channels. Just configure them in the pre-amp settings of the channel to the right inputs and put them in the strip you want them to be. This is also great for panning issues. (remember that ganging does everything in absolute way, including panning… very useless for stereo channels)
TIP : Don’t do it thru the I/O screen. that is because the Input channels don’t show that they are patched stereo channels. (is a visual bug)
GLD80 
