
OP, you already HAVE the controller you need!! Wait a minute! I just realized from OP's last post: OP has a 3-pack of Lian Li fans WITH a CONTROLLER that is managed through their L-Connect software tool. I will try to contact that maker and get the facts. However, I am not yet sure the stories I heard are true. I have been told of such a device from a third-party accessory maker that you can buy without changing your mobo. You need an actual ARGB controller for that type of signal. So when you use a signal translator box, the ARGB lights can be fed the proper signals to generate all the displays a PLAIN RGB system could do, but it will never get signals to generate the fancier things that ARGB lights can do when fed by an ARGB Controller. Hence the mobo 4-pin plain RGB header and its Controller does NOT know how to send out signals that its intended lighting device cannot generate, anyway.

As you are aware, a plain RGB system cannot generate many of the fancy multi-colour displays you can get from ARGB - things like a static rainbow, or even a rainbow chasing itself down the light strip. HOWEVER, there is a big limit that is important to you. There are a few ARGB Controllers and converters like CountMike has linked to above, and they CAN convert from the 12 VDC 4-pin plain RGB signal system to proper signals and power for a ARGB system.
