As for the var. inputs:
It should be easy to add some GOOD QUALITY little pots to the rear panel, like ALPS or BOURNS.
Adding 1-10 fascias will look very sexy!
But if you're uncomfortable doing this forget it as it may jeopardize the warranty!

I can confirm the crossover problem.
I have 2 expensive KEF Reference speakers and bridged the (very complicated) low channel crossover filter, placing an active Behringer crossover before my final amp.
Sound was awful, very peaky and wobbly.
Asked KEF, they said the passive xovers should not be disabled, since they were measured in together with the rest of the speaker.
So I just enabled the Xovers again and removed the active ones.
Sound is quite lovely, MUCH better than before biamping- very exact stage placement, deeper bass and very clean mids.