Hi DJ,
There are so many ways to control the density per object (and even per particle!) that I don’t know where to start 
First of all, if you assign a Standard Material to a PRT object, the Opacity channel will be used to modify the existing density. For example, if the Density of a particle is 1.0 (which is the default with PRT Volume for example, or for PRT files loaded in a PRT Loader when there is no incoming Density channel), if you set the Opacity to 50.0, you will get a Density of 0.5 (50% of 1.0). Since the Opacity channel of a Standard Material can be assigned an Opacity Map, you can even control the Density with maps.
Also, we have a simpler Krakatoa Material which has only the controls relevant to Krakatoa, including a Density control. If you assign this material to a PRT Volume or PRT FumeFX, you could tweak the Density per object.
On top of that, the PRT objects support the Max Visibility track as a Density multiplier, So if you tweak or animate the value, it will affect the Density of all particles of the object. While the Object Properties UI limits the visibility value to the range 0.0 to 1.0, using TrackView you can specify ANY values for Visibility, including negative or higher than 1.0. For example, setting the Visibility in the Object Properties to 0.01 will render the particles 100 times less dense. Opening TrackView, adding a Key to the Visibility track and setting the Key’s value to 100 will render the particles 100 times more dense. But since these controls are not “in your face” but hidden in the Object Properties dialog, I don’t recommend using them in your case.
The Advanced method for tweaking Density would be the Krakatoa Channel Modifiers. You add a Krakatoa Channels modifier to the stack of a PRT object, open the MagmaFlow Editor and set the Output node to Density, the Input node to Density, then with the Input node selected, hit the * key on the NumPad to add a Multiply operator node, then with it selected hit Ctrl+1 to create an Input node with value of 1.0. Now tweak its value up or down to scale the Density (you can keyframe it, too). You can right-click the Input node and select “Expose Control” and the multiplier will appear in the Command Panel as Custom Attribute of the Modifier so you can close the Editor and tweak the density directly from the Command Panel. In the MagmaFlow editor, you could set up complex relationships between channels, for example control the Density by Age/LifeSpan, Speed, Position or whatever. See this tutorial for more: thinkboxsoftware.com/krak-ma … ng-by-age/