Hi,

This is tricky because in Maya, a shape cannot compute two outputs (This is limitation for Maya, Max can handle it) at the same time, but this is totally possible and simple to do.

Assuming you have a single set of guides and you want to derive two hair objects from it, do the following:

• Create a hair object with one Hair From Guides operator,
• In Edit Guides, create two Per Root channels. Let's call them CH1 and CH2 (Or just paint a "baldness" map as you suggested). See how to work with Guide Channels HERE.
• In Hair From Guides, select CH1 as Distribution Channel. This will generate and interpolate hairs only on the guides with white values in CH1.
• Now select Edit Guides, expand the Ornatrix menu on top (Maya toolbar) and check the checkbox called "Branch Mode". When this option is ON, any operator added will be added to a new branch, which will output another hair or guides shape.
• Add a new Hair From Guides operator from the menu. Ornatrix will ask if you want to create a new branch, click Yes. This created second hair shape. Now you have two hair shapes branching from the same Edit Guides operator. Meaning that any brushing made in Edit Guides will affect both hair objects. Multiple branches will be represented this way in the hair stack:

*We are working on a better way to represent branches.

• In the second Hair From Guides you just added add CH2 as Distribution Channel. Now you have two hair objects driven by the same set of guides. This is how it looks: 

And this is what you can do:

You can do the opposite (Driving a single hair object from two sets of guides) using the Merge operator, which will merge two Ornatrix objects into one. 

Jeordanis Figuereo (Product Designer. EPHERE Inc.)

I just found this. How this can be apply to 3dsmax?