In case of problems with multi-channel sound reproduction while using Elmedia Player, pay attention primarily to these 2 things:
1. Is the audio equipment that’s connected to the Mac configured correctly? The audio equipment can be configured, using a system utility called “Audio MIDI Setup”. You can read more here. 
2. The audio/video file being played must have multi-channel sound. The number of audio channels of the file can be viewed using Elmedia Player by opening its Media info.
From the main menu, go either to Elmedia Player -> Preferences -> Audio or to Audio-> Audio Device / Audio Channels, and select the required audio device and the proper number of playback channels. 
If the playback issue is still unresolved, you can try the following steps:
1. Go to System Preferences -> Sound -> Output, and select your Audio Device as the device for sound output.
2. Access the Audio Device menu in one of these ways:
- Elmedia Player -> Settings -> Audio -> Audio device
- Audio -> Audio device and select Default Output Device.
If the problem occurs when playing surround audio that’s encoded in AC3 (Dolby Digital) or DTS (Digital Theater System), it can be solved by enabling/disabling “Passthrough for hardware decoders: Enable for AC3 or DTS” in the player settings. Not all audio devices can decode AC3 and DTS.