Thanks for the fast response and great tips to try. This thing with nodes really is a brilliant idea, and makes a lot of sense. I just never thought of ejecting the output node.. Now I've figured out that you can do pretty much the same routing as in any advanced DAW, but with fewer menus and settings!
You could try this: enable the metronome in AUM, load the various apps in their channels, but don't use any insert effects etc just their clean output. Now start playback on all and make sure Link is enabled in all apps. Now listen to each one and compare it to the AUM metronome.
I tried to make it as flexible as possible, coming from a background of using lots of analog mixing consoles, patchbays, outboard effect gear and modular synths :)