Sounds like you purchased a set of cables from China. (just a supposition).
OFC cables historically take longer to break in. What I would have recommended is a set of ribbon cables that use "OCC" solid core copper (with or without silver plate) Silver plating always tends to accentuate the upper frequency spectrum.
I have a very flat audio system response curve. I avoid plated cables and always go with "OCC" solid core copper. You will find that most of the harshness will be gone right out of the box. If you are careful in your search, you can probably find good speaker cables form CHINA fabricated from "solid core OCC copper". Beware however - - - sometimes the ads twist words around. Double check anything you buy. Personally, I have moved past CHINA for lower cost quality cables and have mine custom made for extremely low prices. All my cables are "OCC" copper. I have a wonderfully smooth sounding system, without spending a fortune. VANDERSTEEN speakers should produce excellent quality sound and imaging, but the rest of your components need to be of equal quality. One weak link in the chain can kill the whole effort.