What version of the FMOD integration are you using?
Unfortunately, using an object spatializer you cannot use Live Update to monitor the output. All the signal after the object spatializer are passed to the system and is no longer controlled by FMOD.
There are a couple of settings to check before you can get 7.1.4 output:
In FMOD Studio Preferences: set the build speaker mode to 7.1
In Unreal, FMOD Output Format to 7.1.4 and set the Output Type to a type that supports 7.1.4
With these settings and an object spatializer, you won’t be able to use Live Update to monitor the output but you should be able to hear the ceiling speaker.