I think you should check out zipBoard. Like you've mentioned, it's built exactly for the purpose of leaving comments and annotation on your course, whether a SCORM file or an HTML one.
You can upload the course package to zipBoard and then invite your stakeholders onto the project. Else, if you'd like to get feedback without getting them to sign up to the course, then you can just share a link with them where they can submit feedback and review the course.
You can see a sample course and how it works here.