@Chimpware, not surprised it affected the reliability... I can't recommend doing any wiring like this... For those who are interested, I'd be happy to send them the schematic of the 'output' driver. Basically, we have a 5 V supply from the USB power supply that is connected to a 36ohm resistor and goes to the center pin of the jack. the outer connector is connected to a switching FET that when turned 'on' by the blaster, switches it to 'ground'.
I would suggest that a small opto coupler or similar may be the best way of interfacing to these types of devices...
Mat