I don’t think there is a difference in PiezoDN quads across platforms. I have made plenty of QTR curves (non-PiezoDN) for a couple of friends using Windows over many years with never a problem. On the other hand, that might be something that you could test yourself. Try doing everything on just one platform – I suggest sticking to the Mac.
Until now I have never heard anyone describe a standard QTR-Create-ICC ICC used in PiezoDN behaving the way you say yours are. It should definitely not be adding density to the highlights of the negative. This strongly suggests that you are doing something wrong somewhere, but without going over it all step by step from the beginning I don’t know how to identify the problem. And it might turn out that you are doing anything wrong at all.
I need to take a break from this (the forums) for a week or so, if I can manage to stay away. Try what I suggested above and see if it makes a difference.
Good luck