Ah, so that was it.
I'd forgotten about that direct routing mode that 'hides' the software playback channel section, possibly because I can't remember ever having used it.....
At least, that's my excuse.
TM is probably the most comprehensive software-controlled mixer there is as far as routing anything anywhere goes but the downside of that is the complexity of it all. Still, could be worse, at least you can see mot of what's going on at a glance and unlike most digital mixers there's virtually no menu diving required.
And you even get a huge printed manual as well.