It seems this would be a theory topic, since none of you apparently have Bryce available to try it out on! Goddamn inneficiency, but the flow of ideas is good. Instead, I'll answer your question, Johnpenn. I've myself run into some gnarly volumetric problems in Bryce using booleans. It's because in Bryce, there ARE no booleans. When you group objects together, Bryce doesn't create any real geometry like we all originally hoped. Bryce uses a filter process similar to what you wuld do manually in Photoshop to create objects and whatnot, and THAT is why it doesn't work on volumetric materials. The problem doesn't lie in Bryce's internal programming, rather in the fact that volumetric matrials have VOLUME. So, the Density, Fuzziness, and Edge Softness play a huge part in how your render will work. If you're animating, I suggest trying a regular procedural approach. If you're doing stills, then honestly sir there's no reason why you need to group ANY of these objects. You're playing with FIRE, not matter. Fire is photons, so you should focus on light-sensitive materials as opposed to regular volumetrics. If I seem abrasive, I apologize. But last time I checked, you couldn't grab or hold fire. Unless you're a DRAGON (grins).