The easiest way would be to get an oscilloscope and look at the waveforms from the sensors. It sounds like one or more still aren't working right.
Are the tone rings clean? Nice sharp, non rusty edges?
Because the rear ABS sensor is inside the differential I can't see how the parking brakes could have anything to do with it.
Check out this thread:
Trying to troubleshooot Bosch ABS2
Annoyingly the ABS system has extremely limited diagnostic capability. It can throw the light when it thinks something is really wrong, but it has no built in way to tell you what sensor is bad. (Unlike other modules in the car that can give you blink error codes).
-J