bad news is I have been trying to track done a Set of HSK163's.
Cannot seem to find them, So your option will have to be the next progression.
But to answer your question. You get a far better midbass driver. So better kick in the front, always a bonus.
The Mid is made better including better materials. It has a smoother sound including a wider range to be able to play.
The tweeter are there 20mm Tweeter. Suppose to be one of the nicest laid back tweeters around.
Additional Note the HSK mid is smaller than the ESK series. So you will be able to fit them in your doors no problems.
I know of many people that have gone from the HSK163 to the Mille, But they end up wanting to go back to the HSK's.
So that has got to add for something, right?
These are only observations I have made and info I have gather inregards to these speaker options.
As we don't have Hertz available over here where I am. I do alot of research and read reviews with songs I know.
Compare to what I have been running in the past.
So Personally I cannot offer to you how your choice would sound.
How about sound deaden your doors, after that if you still feel like getting more from your system. Then get the next level up of speakers.