According to the continuum manual:
To connect both a Midi Keyboard and Continuum Fingerboard to Kyma at the same time: The Continuum Editor must be running, it must have the Midi keyboard as its ExtDevice input, the Keyboard must transmit on Midi channel 1, and the Midi Routing in the Continuum must pass Midi In to Midi Out.
The Editor routes the ExtDevice to the Continuum, and the Continuum moves channel 1 KeyOn/KeyOff messages to high-numbered Midi channels, one note per channel.
Some further observations...
I haven't ever been able to configure the midi channels that the continuum uses and I don't think you can. It normally starts from MIDI channel 1. If you have 8 notes of polyphony on the continuum it will use channels 1 - 8. And it uses CC messages to transmit the Z-axis.
If you're using something like the Behringer BCF-2000 with kyma, then kyma reserves CC's on MIDI channel one for that. Which means if you try using the continuum and BCF-2000 at the same time with kyma you'll find all the notes that get assigned to MIDI channel 1 are missing. The continuum has a special kyma midi mode to fix this. In that mode the continuum starts at channel 16 and allocated notes from 16 down and so you don't get the clash on MIDI channel 1.
The CME xKey I think uses a single midi channel and transmits pressure using the Polyphonic Aftertouch midi message. You can set the global midi channel for the xKeys. If you were trying to merge the midi streams of the continuum and the xkeys yourself somehow (in kymaConnect?) then you'd want to make sure that the channels don't clash. But the continuum manual suggests you let the continuum editor merge the midi signals for you, in which case you need to set the xkeys to channel 1.