Route Audio From One Instrument Into Another (Eg Sampling With Maschin

Using Maschine, but it could be any sampling VST instrument…

I want to route the output of a track into an instance of Maschine (plugin mode), so that I can sample it within Maschine.

In ableton, logic etc, it’s easy, Maschine’s input is visible as an output destination on any track channel.

Have RTFM, used the search function, etc… I just can’t see how to get this done in Renoise?

Well, you have done your best, but unfortunately, Renoise itself does not support this option like that.
A side-trick could be using the VST version of Energy-Xt or use ReWire to route the output to the ReWire master and route it into a plugin there.