One of the unexpected benefits of the recent soldering disaster is the discovery of a worthy source of drivers: Newark. It turns out that, on the TWFK, Newark has the item back-ordered but charges $16 less per driver than Mouser. A $32 savings in costs of materials is nothing to sneeze at. Go, Newark!
I've also run across a rival to Knowles Acoustics: Star Micronics, maker of the RBB-O4A/O4B/O4C/O4D/O4F-PS drivers. Of these, the B,D and F series look like the best matches for hi-fi audio, with impedences of 33 for the B and F, and 15.5 for the D. But the proof is always in the pudding. Has anybody heard any of these drivers? Only the C and F actually have "spouts." I'm not sure they're an actual improvement over KA so, for now, I'll probably stick with Knowles Acoustics.
UPDATE 7/1/09
The replacement parts have arrived. Time to get back to work.