You cannot mix the two like that. The low impedance output of the 85 will load down the passive pickups.
You will have to run the single coils through a preamp to convert them to low impedance and then mix them with the EMG-85.
One solution is to use an EMG Afterburner or PA2. The way you would do this is to have the two single coils on one side of the 5 way switch, and then the output of that side of the switch would go to the preamp. The 85 would be on the other side of the switch.