Following the tutorial to create a search and result set is probably the best way to get going on this. The form that you have with the dropdowns is no different than a form where the user would enter those values, it will post whatever you have as the value from these lists. If the value from the list is not what you would like and you need the label instead you would have to incorporate some additional js to set the selected text to another hidden form element. You can then use this other hidden form element in the search server behavior.
I'm including an example of some js code that will set the value of a hidden form element to the selected text from the list.