Go to your Input Setup and check Preset for each Input device. You can set the Mode to None so that it does not apply a given mode automatically when it receives a given signal. The Anthem is just applying the DTS Neural:X up mixer to the DTS signal here. Always check the input signal display to make sure the appropriate signal is being output from the selected source device.
DTS:X signals cannot be up mixed, though lossy DTS 5.1, lossy DTS HD HI RES 7.1 and lossless DTS HD Master Audio 7.1 can all be up mixed using DTS Neural:X. Dolby Surround is Dolby's up mixer. Different AVP/AVRs will have different restrictions concerning cross up mixing of Dolby and DTS signals. Like DTS:X, Dolby Atmos signals cannot be up mixed. If the speaker configuration is not compatible with Dolby Atmos, Atmos metadata will not be processed and the incoming signal may display as DD+ in the case of streaming or DTHD concerning discs with a Dolby Atmos track.
As was mentioned, make sure the speaker configuration matches the actual speakers in use or you might actually process and output signals to speakers that aren't actually there rather than have the Anthem reroute signals to speakers that are actually being used.