If it's power you're after then your best bet is a de cat with no middle box with a single back box.
I had this kind of set up on my
ibiza but now I have a full straight pipe from the turbo and it makes the wooing noise you're talking about with a very loud growling note. I don't see any change in power either but a bit of back pressure should give more power in theory and be less harsh on your turbo seals etc.
Any 1.9 or 2.0 TDi apart from most 90's will "choo" with the silencer boxes removed but it will be louder without the cat as well. If it doesn't then you've got a boost leak or your turbo isn't boosting properly and is probably on it's way out.
A smaller diameter pipe will give a longer lasting higher pitched "choo" where as a larger diameter pipe will give a shorter deeper pitched "choo".
Hope this helps, welcome to the diesel straight piped land that is Northern Ireland