What I'd like to be able to do is use one TTL master flash, perhaps connected directly to the camera with the camera in Av/Tv mode, and use a slave flash (or more than one) as either optical or wireless slaves. What I'd like to be able to do is get the non-TTL flashes to trigger while the camera is getting its TTL reading, as well as triggering again when the shutter is open for capturing the image. Is this possible?
I've read this question and accepted answer on mixing flash usage modes, but I'm not sure it really answers my question.
I understand that I can set the Non-TTL flashes to ignore a preflash (I'm using Yongnuo YN-560 flashes), but can I get them to fire for both a master preflash and a master flash? I have wireless triggers available (non-TTL) which I can use if these would help.