Looks like it should work OK.
On my board, I connected pin 4 (Channel 3 Detect Enable) to pins 9 and 10 (CH3CODE0 and CH3CODE1).
Pin 4 is an open collector drive so it should not matter if it is grounded. I do not think it will matter to the operation of the board.
The only other issue I had was too much gain, it caused spurious counting when no input was attached.
All was fine if any signal in range (frequency and amplitude) was there.
Working on an updated version now that has an on board shield to see if that helps..
ed
