So, I completely winged it and replaced the weltronics tweeters in my PC desktop speakers and it worked wonderfully. They are smaller than the the recess by about 1/8", but were easily mounted by driving the screws on a slight angle. I have no idea what the sensitivity of the Weltronics was, but the TBs have certainly improved the sound, even after only 10 hours of pink noise.
http://paulhanley.com/audio/tb_bx5.jpg
http://paulhanley.com/audio/tb_bx5.jpg