Hi,
https://www.multiplex-rc.de/Downloads/Multiplex/Bedienungsanleitungen/1-00151-bedienungsanleitung-multiplex-cockpit-sx-12--de-en-fr.pdf
when you download the manual for the SX12 you get a "general" manual which mentioned that the main technical difference between SX7, SX9 and SX12 are the channel numbers and the position switch AUX5 and AUX6.
The second difference is the preinstalled MULTIGYRO CSX, which seems you can optional buy for the SX7 and SX9.
It seems that the SX12 has the newest firmeware. So, for the moment, the SX12 will have the advantage of the newest firmware features. The MPX-Team mentioned allready in the forum, that the SX7 and SX9 will get a firmware update, too.
But these are only my observations from the distance.
I think on long-term i will sell my Royal Pro and will replace it with the SX 12.
Bye Andreas