DPX maybe? I've never exported DPX before because it's not an option on my copy of CS6 - maybe that has to be downloaded separately?
Your CS6 'Format' dropdown list should include DPX:
Among the options you listed, DPX would be my choice.
Be certain the dupe house can accept these files before proceeding.
I would like to be able to offer them a few different options and see what they prefer
I'd go the other way. Ask them to give you a few export options that they know they can handle.