I finally found an excellent and ~affordable digital crossover, the Yamaha SP2060.
I wonder if the Orion and NaO could be offered with a guide for the values (time delay, gain, crossover slopes and frequencies,helve and parametric equalization) to apply, using the Yamaha (or another?) digital crossover between preamp and power amps?
Specific DIY active crossovers are complex to make, and lack flexibility.
The sound quality of, for example, the Yamaha, is excellent: 24 bits/96kHz conversion, and the sound is very transparent - I compared 'with' and without' crossover, everything in neutral position, using B&W N805 speakers, and I am not sure I can detect the difference.