Well, even more noise reduction accomplished. After talking to Ron, it became obvious that the hum canceler had to come out front, so Mike from Woodsongs routed a nice hole in there. Ron also informed me that grounding the cover via a wire is trouble, because of its width to length ration, it can act as an inductor, so I got rid of that and installed tabs of copper shielding.
Got it home, tuned in the hum canceler to the best balance with the other pickups and it was indeed much quieter. It would be barely noticeable in a mix, even from a recording made sitting in my basement studio in front of the computer, etc.
Then came the leap of faith. Ron told me that the big problem with having the humcanceler in the body was all the shielding around it. While shielding protects the wiring, it also, as far as I can understand the brilliant mind of Mr. W., disperses the radiating fields of electromagnetism floating around in a very disruptive way so that the humcanceler is seeing a very different EM field than the pickups are. In fact, any metal does this, it doesn't have to be shielding, connected to any part of the circuit or otherwise have an electronic function. Even bridges, metal battery covers, etc., do this. What does it less than the copper shielding inside my bass is, wait for it, silver paint! Silver paint does its job as a shield but is thin enough that it doesn't create havoc from ambient fields.
So, armed with that knowledge, I decided to see if I could take things a step further. The luthier, Matt at Woodsongs, who had installed my Alembic pickups had very carefully, and with a large amount of skill, had shielding the pickup cavities. It was a thing of beauty. But, heeding the words of Ron, I yanked all that stuff out of there.
I'll be, well, you know what, if it isn't even quieter still! Removing shielding to decrease noise seems counterintuitive, but in this scenario (since the pickups are already shielded), it really made an audible difference.
I'll have to post a picture of the front.
Next experiment at another time: try out the old pickups. The new humcanceler is there to stay, but apparently it should work.
Much gratitude to Ron, and James, and Mica, and Susan, and Mary, and all of them. It is a wondrous thing they've got going on there.