The DTH was Peavey's attempt at a pro-level concert box with a large format 2" horn and horn-loaded mid. Replacing the horn loaded mid with a larger front loaded driver will leave a huge gap in efficiency between the two sections that you will probably not be able to mitigate without biamping the top.
If you don't plan to biamp, you'll be chasing your tail. You are probably best served selling the DTH and moving to a less powerful but more full-range front-loaded box.