They wouldn't look much different tbh, as someone who's used to working with the DOA5 meshes and bringing them to DOA6, they would look the same, especially Ein since he's basically Hayate. Besides the bodies being different with different builds here and there especially with the guys, the faces and hair are the same, just of somewhat higher quality and there's more face bones and the way lighting works in DOA6 it casts upon their skin tone unlike DOA5, but if you use older body mesh parts from DOA5 you'll have to adjust the tone since in DOA6 their tones don't cast the sameI mean normally they would've used their current DOA6 Engine which I know is shitty but who knows what Leon, Ein, and Gen Fu would look like in the DW9 Engine. Perhaps if someone can showcase an example of their DOA6 appearance.
Also I found the various hidden stuns, I'm glad a few didn't make the cut since again some of them are quite disturbing(I'm guessing due to the speed), but some I liked for the variety