KW Street Comfort is not harsh at all! It is firmer than stock spring/shock combos but absorbs hard impacts much better w/o the big 'bang' you get from spring/shock combos.
OP: if you don't want dampers valved with springs just try non rft's with new dampers like Koni sport and set the rear shock rebound 1/4 turn from soft. Skip the fsd's; they're inconsistent.
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