How to control two groups with knobs

Here is an example of a preset that has two knobs, each one controlling the volume of a different group:

<?xml version="1.0" encoding="UTF-8"?>
<DecentSampler pluginVersion="1">
  <ui width="812" height="375">
    <tab name="main">
      <labeled-knob x="100" y="60" label="Group 1" type="float" minValue="0" maxValue="1" textColor="FF000000" value="0.5">
        <binding type="amp" level="group" position="0" parameter="AMP_VOLUME" translation="linear" translationOutputMin="0" translationOutputMax="1.0"  />
      </labeled-knob>
      <labeled-knob x="200" y="60" label="Group 1" type="float" minValue="0" maxValue="1" textColor="FF000000" value="0.5">
        <binding type="amp" level="group" position="1" parameter="AMP_VOLUME" translation="linear" translationOutputMin="0" translationOutputMax="1.0" />
      </labeled-knob>
    </tab>
  </ui>
  <groups>
    <group name="Group1">
      <!-- Samples for group 1 go here -->
    </group>

    <group name="Group2">
      <!-- Samples for group 2 go here -->
    </group>
  </groups>
</DecentSampler>
Code language: HTML, XML (xml)