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 -> Settings -> 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 Settings-> 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 Dolby Digital (AC-3, E-AC-3, or TrueHD) or Digital Theater Systems (DTS, DTS-HD), it can be solved by enabling/disabling “Passthrough for hardware decoders” in the player settings. Not all audio devices can decode files with these codecs.