With so many components, it can be daunting to plan your system. Simplify the task by thinking in terms of inputs and outputs. Count the number of line-level electronic sources going in to your system (MP3 players, keyboards, etc.), and add the number of acoustic sources requiring microphones. Make sure your mixer has at least this many inputs. To determine your output needs, consider how many listening positions are needed. In addition to the main mix, musicians perform better when they are able to hear their performance.