EMIT-k was introduced with the first Kappa series speakers. An EMIT-k can be used in place of an EMIT, but the output level may be off slightly from the rest of the speaker. As cdfac states, however, most EMITs use the exact same diaphragm. So, if you want to maintain the originality of your speakers, you can buy an EMIT-k, open it up and remove the diaphragm, and install the diaphragm in the standard EMIT chassis. Or vice versa. Just be sure to use some sort of jig to keep the halves of the tweeters from shifting and slamming together out of alignment during disassembly/assembly. This will prevent >95% of tears and damage to the diaphragms, as well as most magnet damage (and pinched fingers).