To determine what goes into the BRD and what goes into an SRS, the best place to start is by thinking in terms of who uses the BRD vs. the SRS and what decisions do they need to make from it. If you think of a typical process model, executives must be presented with information following each phase to determine if the project should continue. Based on the information gathered in each phase, the team presents a summary to the executive who decides whether to proceed.
Early in the project, the program manager decided to use Microsoft Excel as the tool of choice for gathering and managing the requirements, each module would have their own set of requirements. It sounded like a good choice to the program manager, since everyone has Excel on their machine and it would be easy to share files amongst all interested parties. I’m sure that sounded good at the time, but it has certainly been a pain for me.