Hi Dave!
We've enjoyed similar journeys with BAT starting out with the VK-51SE preamp. I have no doubt you had experienced great sound with your ATC actives and BAT.
I wonder how the ATC's would sound with an Atma-Sphere MP-1 preamp, upstream?
Yes, the MegaLine III loudspeakers feature an active external crossover...nothing between the monoblocks and DALI, except speaker cable :-)
You're in the UK...right?
-Sam