You should probably replace them with the same B&W tweeter. Substituting another tweeter without modifying the crossover will likely not work or sound right.
I am not familiar with a DM602 SE (nor does B&W list an SE model for replacement parts), so did you mean S2 or S3? B&W replacement parts are available at
http://bwgroup-support.com/partspriceavail.html DM602 series tweeters are available as complete tweeters or just the diaphragms.
DM602: ~$72 complete tweeter / ~$58 tweeter diaphragm
DM602 S2: ~$83 complete tweeter / ~$58 tweeter diaphragm
DM602 S3: ~$109 complete tweeter / ~$83 tweeter diaphragm
Steve