My experience is that the Pyro stain acts much the same with a condensor enlarger as it does with a diffusion light source with perhaps somewhat of an increased effect from the condensor light source.

I believe that the reason for this is what the previous poster alluded to with the mention of branches and edge effects. The condensor light source is collimated and for that reason grain, scratches, and dust on the negative are more noticeable. This leads me to believe that the stain effect (proportional stain) and edge effects are more sharply defined with a more sharply focused light source.

I haven't conducted tests with this other then printing negatives on both sources. In fact this really would be difficult to determine objectively...at least with the equipment that I have.