My setup is Xone 43c plus one Xone K2 plus Traktor.
Xone K2 is a pleasure to map and has enough controls to have 4 decks, if you want.
I have a second K2 but I never use it.
Xone 43c effects can be sent to Traktor via USB and back to a free channel via USB.
However, I want to add RMX-500 for effects to complete the setup.
Why not DB2 or DB4? Because I don’t want any effects i my mixer besides filters.
One thing though – Xone K2 doesn’t have drives and buggy as hell on OSX El Capitan – doesn’t work until you do a shaman dance with Audio/MIDI setup. Thankfully it only needs to be done once after you plugged it in.