I see, can't comment about shadow detail since I use the "other type" of negatives (not in-camera negatives) and this aspect is irrelevant with them (each process / paper combination has its own calibration - what you see is what you get...), but I can assure pop pd prints are perfectly doable with a vacuum frame; I did a myriad of them with my NuArc 26-1KS. It's just a matter of controlling the humidity of the paper and the enviroment; after that, it's a perfect print every time. (In camera negatives would require test prints for each negative - this is done once, at the very beginning, with the other type - but that's true for both cases of dop or pop printing...)

Regards,
Loris.