Well...
After a lot of searching, I found a solution.
Here it is:
I used an application called 'SoundVolumeView.exe' from this website:
View / change sound volume on Windows from command line or GUI[
^]
This application is very useful and you can do anything with your audio system.
So I used bellow code in my VBA Excel project to change playback device. It changes my audio system to Omni and set the volume to 100% and makes it unmute.
Call Shell(ThisWorkbook.Path & "\SoundVolumeView.exe" & _
" /SetDefault " & Chr(34) & "Omni" & Chr(34) & " 0" & _
" /SetDefault " & Chr(34) & "Omni" & Chr(34) & " 1" & _
" /SetVolume " & Chr(34) & "Omni" & Chr(34) & " 100" & _
" /Unmute " & Chr(34) & "Omni" & Chr(34), vbNormalFocus)