Active crossover is managed using a Nadja Waf board. A bit of an overkill in my system, as I am only using it with a single input (I2S) and output.
There are cheaper alternatives, like the miniDSP minishark board.
I am testing software crossover, using a multichannel USB card (with the newest xmos chip) : http://www.dimdim.gr/2016/01/diyinhk-xmos-multichannel-32ch-usb-tofrom-i2sdsd-spdif-interface/