Unfotunately i must agree with OP.
Sounds needs to remake in my opinion, current sounds could be ok for some other plane but problem is they doesen't really remind real DB 605 sounds at all. Like op said, current sounds ruins the immersion, it's kinda like flying replica of 109: it looks and flies pretty much like original but sounds like it had some modern engine under the hood. I just can't feel the power of the engine now.
And please, with all respect stop posting comments about helmet and headset, or how recordings sounds different than real life. Yes, helmet will act as muffler, different mics etc. may change sound a bit but they won't change the whole engine sounds to another.
DCS 109 looks awesome, cockpit is best 109 in any sim so far, FM feels fantastic (well theres some bugs but like we all know, beta), it really deserves equally great sounds too. With pretty please :)
Unfortunately i don't own any high quality recordings of DB 605 so these youtube links must do it for now.
For interior sounds:
Exterior:
Of course there is lot's of more in youtube, it's just hard to find good quality ones.