Apart from the fact that the Dalesford driver will not be a simple drop in replacement into the DM2, it's not really viable to replace drive units from one completely different speaker to another. You will simply destroy the performance of the speaker. Loudspeakers are designed as a complete system.
If you enjoy the sound of both speakers then keep them original. If you have a faulty drive unit, look to obtain a second hand replacement (which is not always easy). Possibly change the caps but please don't attempt to swap around different drive units.
If you're unhappy with the sound of one or both of these speakers, get rid of them and buy something else that you like.
Best wishes.