I want to use an on-camera TTL flash and off-camera manual flashes simultaneously. That is, when I press the shutter button, I want my main on-camera flash to fire using TTL and my off-camera manual flashes to fire at once with my main flash via a radio trigger.
Using the off-camera flashes in the optical slave mode is not an option because sometimes they might not be able to see my main flash.
I have (or will soon get) a Nikon D750, a Nikon SB-910 as my on-camera iTTL flash, four manual Yongnuo YN560 IV as my off-camera flashes, and a Yongnuo YN560-TX radio trigger to fire them. I also have four PocketWizard Plus III radio triggers that can be used instead of the YN560-TX, but I’d prefer the Yongnuo trigger.
What setup would you recommend? Perhaps there is a hotshoe splitter that would pass the iTTL signal unchanged to my on-camera SB-910 and also pass the main fire signal to the YN560-TX? Are there any other options?