I don’t recommend using 1 of OT’s 8 audio tracks to generate an audio trigger.
Consider this naïve assessment: a new OT costs 1,350 USD at Elektron’s webshop right now, that makes about 169 USD per track. So if you use 1 OT track for an audio trigger, you’re sacrificing 169 USD of the OT’s worth to perform a utility duty, instead of being available for exciting audio manipulation. Add to that the purchase of a preamp like Gozinta, which sets you back a further 100 USD, then you put down a total of 269 USD for a makeshift sync connection.
My recommendation for a proper sync connection is to get a decent MIDI-to-clock/sync converter Eurorack module, like the doepfer a-190-8 usb/midi-to-sync interface for 180 USD.
If you don’t want to shell out any money (except for the OT, that is), and have a preamp Eurorack module with envelope follower and trigger detector already, then instead of wasting one precious audio track you can try to use the OT’s metronome as the audio trigger (via the OT’s second output pair), but this means you can no longer properly cue OT audio signals, as these would mix up with the metronome audio, which ruins your sync…
…which means that all things being equal I really recommend a dedicated MIDI-to-clock/trigger module.