Explained in another post using the correct underlayment (with floating installation method) has to be the start of your enjoyment of the end result.
When you have one area containing two (or more) types of underfloor you have to start with other preparations: making sure you have one type of underfloor. Example: extension with new concrete underfloor connected to a room which has existing floorboards. Both types of underfloor (can) have a different temperature or moist content and your natural wooden floor will react accordingly: one part of a board when laid on both types could 'go-all-over-the-place' and you could end up with a cupped or warped floor.
Simplest solution in this situation is to install hardboard sheets in the whole area. You could install a DPM on top of the concrete first, that really depends on the moist level of the concrete (if new concrete or screed it is recommended). On the hardboard (=sheet material) use a foam or rubber underlay for sound-insulation and your underfloor is ready for the wooden floor.