You can modulate the original VDB data channels with Ramp nodes:
- Create an aiVolumeSampleFloat node
Type the channel name you want to use as the driver in Channel (like density)
- Create a Ramp node (delete the palce2dTexture node)
- Connect the aiVolumeSampleFloat/OutValue to the Ramp node/V Coord
- You can use the Ramp/OutColor output as an RGB color input in the aiStandardVolume shader (for example Scatter Color)
- You can also use the Ramp/OutColorR output as single channel input in the aiStandardVolume shader (for example Density). So you can use the original ramp modulated density data as density input in the shader.
You can also use the Remap Attribute feature in the aiVolumeSampleFloat node (the Bias is extremely useful).