Replying here in this old topic as the audience is likely informed...

I have a PEAD 125 ducted heatpump and I want to add a Mitsi MAC-588IF-E Wi-Fi controller to it.  The Wi-Fi controller needs to plug into the CN105 connector on the air handler however CN105 is already occupied by the connection to the wired remote control panel (wall mounted). Does anyone know if I can 'simply' connect these two controllers in parallel?  If so, I would make up a 'double adaptor' cable using the bits from aliexpress.

I note the Mitsi website says:

• If you have the optional Wi-Fi Interface connected to the indoor unit then unfortunately the Wi-Fi Interface plugs into the same terminal (CN105) as your current wired controller. As there is only one CN105 terminal on each indoor unit it is not possible to have both a wired controller and Wi-Fi Control.

However Gemini suggests otherwise, pointing to several aftermarket devices that do it.  I guess my question is wether those devices are just glorified double adaptors? 

I found helpful info on CN105 in this post and other relevant info in this 2023 post.