Agreed. All my amps are noninverting. While the polarity issue is interesting and may certainly pertain to the entire 434X family of monitors when moving from internal passive to biamping with a fourth order network, my interest is primarily with Greg's comment about FR at crossover.
When I have some time, I'll run the RTA and see if there is something there that's measurable. Robh, you've been fooling with this sort of four way set up for a while, have you noticed anything and care to chime in?