when the HF driver is typically isolated from the xover by the resistive padding network? Even with those wild mood/Z swings, the xover itself will still be seeing a fairly nominal load. And the HF being padded say 12dB to match the LF, when you are listening to bass in the 100dB range, the HF will be rocking along at 1/16 watt...
Why not try putting a zobel directly across the HF driver to deal with the 450Hz. peak, and see if that helps. Samringing with high order filters...is it due to oversaturation, and isn't filter Q another factor...or something:( Wayne, how about a few words regarding ringing in a reactive circuit...