I have the same problem. I own wiim pro and topping dx3 pro+. When I connect my TV to the stereo system via optical Topping DX3 Pro+, there is no delay at all. When I connect my TV to a stereo system via optical in wiiw pro (analog or optical output) there is a clearly noticeable delay. I chose the pro version of wiim, also because of the presence of an optical input to which I was going to connect the TV, I like to watch music videos and concerts, but this turned out to be impossible, the sound lag is clearly visible.
The only thing I can connect to the optical input is my CD player. I'm disappointed. I don't understand why there is this delay? Is this a feature of the chosen streamer architecture? Can't it be fixed with firmware? I really hope that the amplifier that is coming to me will not have such a delay, otherwise it will be an epic failure!