If the square wave clock is at the BPM rate, you should be able to use that signal directly as a gate in your Kyma Sounds. For example, let's say you are receiving the clock on input channel 8 of your audio interface; then, in the Gate field of your Sound, you could paste:
AudioInput8
or, if you need voice stealing, you could use
AudioInput8 L withVoiceStealing
Depending on what your clock signal looks like and how/where you want to use it in your Sounds, you may need to do additional processing on the clock (possibly a Threshold, ScaleAndOffset, InputOutputCharacteristic, etc), but this would be a good first test.
You could also do some tests comparing it against using Ableton's MIDITimingClock to test whether passing the clock through the analog converter and back to the digital domain introduces a delay.
Please let us know how it goes. Thanks!