Those dampers you bought were designed to be used with oe sport susp / zsp springs. Folks have used them with the PS springs and say they still dampen the susp effectively. If you decide to do that make sure you get the correct bumpstops for the PS springs. The bumpstops that came with your dampers are too tall for the PS springs.
BMW PS with or w/o PS springs>ST c/o IMHO
2007 E90 335i, TiAg, 6AT, ZPP, ZSP, ZCW, 6FL, HD
Quaife lsd, ETS fmic, GIAC s/w, Dinan intake/exhaust/oc, KW/GC/M3/Meyle susp, Apex Arc 8, Mich PSS