Leslie V. answered 03/20/19
English Pronunciation Expertise, Experience and Enthusiasm
American English speakers use intonation for emphasis. In your examples, *do* would always be stressed. If it is unstressed, the flatness conveys lack of enthusiasm.
You say "you can *just* stress the modal verb itself" but using your intonation (musical tone of voice), in my opinion, is the most elegant way to express emphasis, as well as reluctance, enthusiasm, acceptance, uncertainty, frustration etc.