Finally got around to installing everything; RE 6.5c front, RE 6.5 rear off a Planet Audio BB175.4, 2 RE SEx 10s off a Planet Audio RXD1400. Gains set with a DMM, HU volume set at 30 w/ eq flat and I have no audible distortion.
I talked to a local KW dealer as well as a KW customer support regarding HU clipping point and rca rms voltage and got different answers from both.
Dealer: HU clips at 32/35 @ ~2.5-3v rms front/rear, 32/35 @ ~2.5-3v subs +2
CS: claims the HU will not clip 35/35 @ ~4.5-5v
Haven't had a chance to check rca voltage meself just yet.