Thanks for all the responses. This is a great forum. The FB1's sounded lovely with my old Roland power amp. I might experiment with the biamping* and run some sweeps to see what is happening to the freq response and sound, before selling the second amp. (It's in my nature to test things for myself. It doesn't mean I'm ignoring the advice here - just attempting to verify it) My room is charted from several well defined reference positions. Everything I have read indicates that bypassing internal x/o's and attempting to biamp a system not specifically designed for it, rarely if ever works well. Your experience Horseface, seems to follow that pattern.
In reading the responses, I realized that I had been careless in my thinking. The tweeter's signal only decreases at 12 db/8va below 3k. At 2k there would be a lot of overlap between the x/o's. A better target freq for the amp's high pass x/o would be something around 200 where the overlap in the 2 x/o's would be minimal, but then there's the phase issues Kal mentioned.
*The amps come as a pair. I expect to sell the 2nd one after some playing around.