You've accurately described how soft patch relates to traditional instruments. All that's required to understand the way soft patching relates to moving lights is that moving lights respond to DMX channel levels exactly the same way as dimmers, except that the level value is being used to control something that isn't a dimmer. Moving lights generally require multiple channels, and so you use Fixture Patch on an Express to assign which Express and DMX channels will be treated as moving lights. Then, when you select those channels (now shown with a light grey rectangle grouping them) the Fixture Box comes up and you can adjust each channel/attribute of the moving light.