Hmm, there's not really a way to do per-voxel particle sampling like that using tyFlow's VDB operators.
The closest alternative would be doing something like loading the VDB data into a fluid containing (Ex: a PhoenixFD grid container), then sampling the values using a Fluid Properties operator. However, it expects RGB data to be stored in a single vector, so even then you might not be able to achieve the effect you want without first doing some channel conversions to combine your separate RGB channels into a single one...
The closest alternative would be doing something like loading the VDB data into a fluid containing (Ex: a PhoenixFD grid container), then sampling the values using a Fluid Properties operator. However, it expects RGB data to be stored in a single vector, so even then you might not be able to achieve the effect you want without first doing some channel conversions to combine your separate RGB channels into a single one...