Analog switches are a solid state alternative to relays, when you want a smaller, lower-power technology that won't wear out mechanically. And, as the name implies, you can use the Adafruit ADG729 Dual 1-to-4 Analog Matrix Switches to connect between two sets of four analog signals, much like 8 mechanical switches. These chips tend to be tiny surface mount parts, so this breakout will let anyone use the ADG729 switch for signals up to 5V, without fiddly soldering.