But it did work before you put it in the rack? I don't have the K-2, but for the Neutron there were small dip-switches in the back, I think, to set the MIDI channel. Does the k-2 have those as well? If so, maybe you need to also remove that little board from the k-2's case and connect it to the k-2 in your Eurorack case. Just make sure it's affixed to the case in such a way that it doesn't short anything.