The Pyle audio router's 4-Digit LED display appears to be multiplexed since it's a 12-pin LED unit. From my lay perspective, this increases the complication.
You have 4 inputs looking at the common pins of each 7seg display.You have 7 inputs looking at the 7 segment pins on the display.
They would not see logic levels due to the LED voltage drops. You would have to disconnect the display.
Really? It's that complicated