Driven by the need for faster time-to-market and reduced development lead-time, large-scale systems engineering companies are adopting agile methods in their organizations. This agile transformation is challenging and it is common that adoption starts bottom-up with agile software teams within the context of traditional company structures. This creates the challenge of agile teams working within a document-centric and plan-driven (or waterfall) environment. While it may be desirable to take the best of both worlds, it is not clear how that can be achieved especially with respect to managing requirements in large-scale systems. This paper presents an exploratory case study focusing on two departments of a large-scale systems engineering company (automotive) that is in the process of company-wide agile adoption. We present challenges that agile teams face while working within a larger plan-driven context and propose potential strategies to mitigate the challenges. Challenges relate to, e.g., development teams not being aware of the high-level requirements, difficulties to manage change of these requirements as well as their relationship to backlog items such as user stories. While we found strategies for solving most of the challenges, they remain abstract and empirical research on their effectiveness is currently lacking.