I can’t find any reference to “Cat 5” insulation.
In any case, in my opinion, it’s better to specify the desired outcome – acceptable noise transmission – than the method.
If the cladding scandal has taught us nothing else, we now know for sure that installers of any building products (and their colluding customers) will lie about the quality of the products they install if they can save money.
Put the onus on the person changing the flooring to get it right. Who’s going to get NCAT to order a floor be ripped up to check that it has the right material under it?
If an owners claims the installed the right material but they haven’t or it doesn’t work, then the neighbour below will have to live with the consequences.
Finally, have a look at this page from the OCN (which, I have just realised, quotes me).
Any timber floor over acoustic underlay is a poor substitute for carpet over quality underlay when it comes to sound insulation. Specify the noise reduction, not the product – if only because a better product might come along and you will have to rewrite your by-laws all over again.