I connected all the red wires as you instructed and the buzz got much quieter but I did get a scratchy blend. I disconnected them again and the buzz came back and the scratch went.
So I can confirm that the scratchyness in the blend pot did go away when I disconnected the red pickup wires again.
A ground wire between the bass, treb, an volume had no effect for me.
Found these Aguiler wiring diagrams, one of which (page 1) looks just like my wiring EXCEPT there is no ground connection between the volume and blend. Maybe that's our problem? I'll cut mine and see if that works.
http://www.aguilaramp.com/pdf/support_wiring_obp2.pdf