Are MaxxMacro holders compatible with larger chucks?

Yes! The MaxxMacro system is designed for downward compatibility — meaning smaller holders (like the MaxxMacro 54) can be mounted into larger chucks (such as the MaxxMacro 70 or MaxxMagnum).
However, this compatibility is one-way: Larger holders cannot be mounted in smaller chucks. For example, a MaxxMacro 70 holder will not fit into a MaxxMacro 54 chuck.