Communication between AC450 and S7-400

Hello,
I would like to know the best way to connect a AC450 to a S7-400. I have some options, the first option is through a CI532, that way I would use the 3964 protocol.
My second option would be a CI534V02 through Modbus, but I would like to know if it's possible to make the AC450 slave instead of master. And my third and last option is using CI541 through Profibus. Is it possible to communicate an AC450 to a S7-400 through Modbus TCP? Are any of those options that I listed above applicable? Is there a better way to make this communication?
Thanks in advance!