Your PC has HDMI so initially it is likely that the sound streams were being sent to that sound sink.
If you do not use the HDMI connection normally, you can turn off that device from the drop-down menu on the configuration tab.
If that is done then all sound will be sent to the remaining sound sink.
I don't know anything about that E17 desktop unfortunately, but there are several Mixer apps in the repos ...... or you can use the volume control of pavucontrol to alter the volume.