I picked up a Microbrute yesterday and was indeed able to sync it to a Roland TR-606
To get the TR-606 to drive the MicroBrute:
Route Hi Tom or Lo Tom Out from the TR-606 to Gate In on the MicroBrute
In the software configuration tool, set the MicroBrute to use Step On = Gate instead of internal Clock, Sync = Auto, Step 1/16
Set the VCA to use ENV instead of Gate.
Voilą!