Board Thread:Theories and Speculation/@comment-45444155-20200410191621/@comment-4961229-20200414164542

Pretty sure the chakra being amplified in Madara's description is the chakra Hagoromo gave them. They had a small bit of chakra that had the main purpose of linking their hearts and minds together. Instead of doing that they repurposed that small bit of chakra and amplified it with their own mental and physical energies. Thus creating a larger quantity of chakra so that they could use it to fight.