As long as you are ok with ARGB devices sharing the same animation/sequence, splitters work just fine. For example, I have my Helios case front lights and Thor PSU running off a single header on the Crosshair VIII Extreme, using the 1-to-3 ARGB splitter cable supplied with the board (make sure you wrap the pins of the 3rd output with an insulator if you are only connecting 2 things). In the case of fans, they would all be doing the same sequence / effect, which can look reasonable. The alternative is you would need to get a USB-connected fan hub or similar, such as the one supplied with some of the top end motherboards or the Ryujin II AIO (they actually take both USB and ARGB input, so split a motherboard ARGB header into 4 or 6 outputs (not sure if they just send the same ARGB sequence to all ports simultaneously or turn them into a longer LED string). It's basically series vs parallel wiring, with parallel being the easy way that a simple 2 or 3 way splitter cable gives you.