I don't personally use ceiling speakers, Atmos or otherwise(Nick has experience in this type of setup). Without knowing specifically the "multiple ways" that you've tried to connect the back surrounds, it's difficult to judge where the problem lies.
Possibly you should make sure that you've made the proper connections for a 7.1 setup with the back surrounds(as shown on p.49 of the manual)but with the ceiling speakers disconnected. The default amplifier setting is to have 7 channels active, which is sufficient for this setup.
If this results in the back surrounds being active, you can try the next step to power the ceiling speakers. Since this now requires 9 channels of amplification to be active, the amp assign setting(manual p.46)should be changed to 9.1 rather than the 7.1(plus zone 2)which is the default.
