As James says, the bug in version 2.1.4.8 affects the system sound actions.
Here are some examples of how to adjust the system sound, generally.
This is a command group. You can copy and paste all the code into your command tree to test and edit the commands.
<?xml version="1.0" encoding="utf-16"?>
<!--VoxCommando 2.2.0.7-->
<commandGroup open="True" name="Adjusting system sound" enabled="True" prefix="" priority="0" requiredProcess="" description="">
<command id="357" name="adjust system volume" enabled="true" alwaysOn="False" confirm="False" requiredConfidence="0" loop="False" loopDelay="0" loopMax="0" description="">
<action>
<cmdType>Sound.AdjustVol</cmdType>
<params>
<param>{2}</param>
</params>
<cmdRepeat>1</cmdRepeat>
</action>
<action>
<cmdType>OSD.ShowText</cmdType>
<params>
<param>OK. Volume {1} by {2}.</param>
</params>
<cmdRepeat>1</cmdRepeat>
</action>
<phrase>Volume</phrase>
<payloadList>up, down</payloadList>
<payloadList>3,5,10,15,20</payloadList>
</command>
<command id="358" name="set system volume to" enabled="true" alwaysOn="False" confirm="False" requiredConfidence="0" loop="False" loopDelay="0" loopMax="0" description="">
<action>
<cmdType>Sound.SetVol</cmdType>
<params>
<param>{1}</param>
</params>
<cmdRepeat>1</cmdRepeat>
</action>
<action>
<cmdType>OSD.ShowText</cmdType>
<params>
<param>Setting volume to {1} %.</param>
</params>
<cmdRepeat>1</cmdRepeat>
</action>
<phrase>set system volume to</phrase>
<payloadRange>1,100</payloadRange>
<phrase>percent</phrase>
</command>
<command id="359" name="mute system volume" enabled="true" alwaysOn="False" confirm="False" requiredConfidence="0" loop="False" loopDelay="0" loopMax="0" description="">
<if ifBlockDisabled="False" ifNot="False">
<ifType>(A)==(B)</ifType>
<ifParams>{1}&&mute</ifParams>
<then>
<action>
<cmdType>Sound.Mute</cmdType>
<params />
<cmdRepeat>1</cmdRepeat>
</action>
<action>
<cmdType>OSD.ShowText</cmdType>
<params>
<param>OK. Muting volume.</param>
</params>
<cmdRepeat>1</cmdRepeat>
</action>
</then>
<else>
<action>
<cmdType>Sound.Unmute</cmdType>
<params />
<cmdRepeat>1</cmdRepeat>
</action>
<action>
<cmdType>OSD.ShowText</cmdType>
<params>
<param>OK. Unmuting volume.</param>
</params>
<cmdRepeat>1</cmdRepeat>
</action>
</else>
</if>
<payloadList>mute, unmute</payloadList>
<phrase>system volume</phrase>
</command>
</commandGroup>
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video demonstration showing how to copy code into your command tree.