Other than the magic sword mentioned earlier in the thread it was mentioned in short story on zenos as a child that he learned to use aether infused crystals for aether based attacks, similar to how one would use aether infused cartridges as a GNB from an outside source if they can't aether infuse them themselves. A headcanon i have is zeno's big gun-chamber-sheath-thing has aether infused crystals or oils inside of it which magically enhance his weapons artificially.

As for gaius' gold infusion in the description for the gilded magitek armour mount (it's gold coloured in a similar fashion.) says that garleans started using gilded plating on such machinery to make it more resilient to magic attacks, i can only assume it's the same for gaius' armour. As mentioned above the orbs on the armour collect data from the wearer without their knowledge and can function similarly to a job crystal and there is also a spyglass on the helmets which serve to not obstruct their third eye.