2000 A6 2.7T brake squeal

[kf21857 at comcast.net]

I have been away from this list for a while so this is my first post in several years.  Not that I don't like you guys, but nothing has broken that I couldn't figure out with the help of my trusty Bentley manual. 
 
Last summer I finally took the plunge and traded up from my 90Q20V to a clean 2000 A6 2.7T with 6 speed manual.  Except for the usual problems with window lift cable attachments, failing instrument cluster display and oil dripping on the right turbo, it has been very enjoyable.  Recently I noticed that the front brake pads were getting thin so I decided it was time for a brake job.  These are the heavy duty brakes with 4 pads per caliper, same as on the Allroad and (I think) S4.  The rotors had been replaced the last time the brakes were done and had never been turned so they cleaned up nicely and are still well within limits.  Everything went back together with no problem and I installed a set of pads from Blaufergnugen ("Hi-Performance Street Brake Pads, Low Dust, No Squeal").  The problem is that they squeal like crazy, not under hard braking but just as the car is about to stop rolling.  Actually more of a deafening screech that causes people in nearby cars to turn around to se
e what is happening.  Sometimes I resort to using the hand brake to bring the car to a complete stop.

I have taken the pads out twice and sanded them to remove the glaze.  Once they warm up after a couple of miles and a few stops, the squeal comes right back.  Because of the locating pins, there is only one way the pads will go into the calipers so no question of things being assembled correctly.  I even tightened up the metal fingers that hold the pads in place, thinking that maybe one of the pads was chattering.  I did notice that the Bentley refers to removing protective foil from the backing plates and that the old pads seem to have the remains of some kind of black goop that apparently stuck them to the pistons.  The new pads didn't have this.  Could this be my problem?  Has anybody else encountered this?  I have done quite a few brake jobs on various Audis over the years and I am not a novice at this but this has me baffled.  Should I just bag it and try a different set of pads?
thanks,
Dave