Requirements management and agile / scrum

In software development, it is quite common to use agile / scrum. In this approach, the user requirements are elaborated in user stories. Subsequently, these are specified in scenarios, also called use cases. The user story is focused on the happy flow. The scenarios / use cases detail the desired behavior in case of deviations and exceptions.
How does this match with requirements? You could argue that the user stories / scenarios / use cases are the requirements. However, if you still have a set of "loose" requirements, it is useful to link them to the user stories. Most likely the conclusion will be that there are missing user stories. It is also wise to walk through your business processes again, and map the user stories to the business processes. So you're sure you're beaten by not supporting critical processes...
To manage this effectively and consistently I would recommend to use software developed for this purpose, and not mess with self-built solutions in Office. Use that specific software from day one, because the longer you keep messing with Office, the harder it is to migrate ..