Just to be absolutely clear (as I'm not an electronics expert) - if I find that I need to power multiple IR sensors on an 8/8/8, i add an external 5v (3.5v?) psu across the power and earth connections on the sensors, and disconnect the sensor power connection from the 8/8/8? Or doesn't disconnecting the power lead matter?
(My 8/8/8s sit at the end of a powered USB cable connected to a laptop, and sometimes I use some older IR sensors that I have laying around. More than 2 sensors either stops the whole thing working, or the sensor signal becomes very noisy)