Hmm, I am not sure. When using PCF8575, as I mentioned above, since it uses weak pull-up by default all channels are HIGH at start-up, so what I did was to use a PNP transistor per channel to reverse the logic, such that at startup the output becomes low. For this to work I think you will need a pull-down resistor at the output, otherwise the output will be in high-impedance state instead of low.