One last post on the #calfstudiogear story:
the X-Overs are pretty much the only ones I still use quite frequently to mess around with provisional active speaker setups (#CalfJackHost, multichannel Interface into multichannel power amp).
So I wanted to check the notching out of frequencies due to phase issues as mentioned in the #Ardour forum.
All I found is that they behave pretty much as I would expect them to. Linkwitz-Riley 4th order, 4-band X-Over at 100Hz, 1000Hz & 5000Hz. Screenshot: