The logic signals sent to the triac are +3.3V (actual voltage may be a bit lower due to the properties of 74HC595 shift register), and are activate high. You can solder a wire from the triac’s gate pin to direct the signal to external boards.
If your external board requires +5V or higher signal, you can replace the triac by an NPN transistor (like 2N3904) and then the station port pin will become an open-drain (which can be pulled high to any voltage between 5 to 40V) with active-low logic.