yep, this is the most common way of using modules. It's more flexible. But you can apply sliders to any specific layers. Here is a way to do it.
1. Go to the module editor (menu modules > Editor)
2. Add a new module (button at the bottom right of the editor's window)
3. Now you have an empty module window and you face the interface editing tool.
4. Drag and drop a slider from the controls library (bottom) to your window.
5. On the top of the editor, there are options for the selected control. We will route this slider's value to the X position so we need to set min and max values in order to move your media more than only 1 pixel. You can set the min value to -640 and max to 640.
6. In that same area, click on the keyword connect tab and enter 'ctrl_layer_position_x' (without the quotes) in the To textfield.
7. Choose on what layer you want to apply the keyword in the In popup menu.
8. Save all changes (menu Modules > Save All changes.
9. Restart the module (menu Modules > Restart)
10. move your slider and see that your media is moving depending on the position of the slider.
11. Repeat steps 1 to 10 for the Y position using the keyword ctrl_layer_position_y
12. Repeat steps 1 to 11 if you want to have two more sliders to move an other specific layer.
Yay, your first module
Of course, this technique works the same with horizontal or vertical sliders, also with knobs.