The ChromaSense Option includes a control module and one fixture with the option of adding one additional fixture. If you want more than 2 fixtures in your steam shower, you need to purchase 2 ChromaSense Options, each with control module and one fixture, and then add up to 2 (1 each) extra fixtures.
Why 3 fixtures? Is your goal to brighten the room or are you concerned with the intensity of the chroma lighting? Your answers to those questions will determine the need for your application.
The ChromaSense option fixture produces roughly the equivalent of a 40 watt lamp and the color intensity is user adjustable. Depending on the size of your shower and how much light comes in from the bathroom light, you may want to consider installing a steam light
if your goal is brighter lighting.
I would recommend reviewing your installation and environment preferences with a Steam Shower Specialist