If I am reading the installation manual correctly, I can connect an OAT to the EMS module for cabin temp but in order to calculate TAS, etc, it needs to be connected to the ADAHRS.
In SkyView, yes. The "system" OAT is the ADAHRS one, although you can add another separate OAT to the EMS connector that can measure any air(ish) temperature (including OAT) you want. On the D10/D100 series, you can have the system OAT hang off the remote compass or off the EMS connector.
