I've created a simple scene consisting of a sphere, box and torus. All three are used as sources in a single popnet. Now i want to render each of these particle sources as different sprites.
Because I have to assign the sprite material at object level, this leaves me only with 1 sprite option??
I've played around with the pop merge and fetch options but didn't get anywhere
You could use material overrides to achieve this. I didn't have the time to look at your file, though.
But in theory you have a unique attribute - like generator - assigned to your particles. Place a materialSOP and set it to override based on point attributes.
If you don't mind using three different materials, which is easier for the start, then just split the particles after the popnet and objectMerge them in to different geometryOBJs. Now you can assign unique materials to them.