When I use fluidsynth, or other multi MIDI-channel plugins, I can’t create a separate track for each of its MIDI channels, like in other DAWs (Logic allows ‘multi-instruments’ which has a separate MIDI track for each channel).
It is a fundamental design question. In Ardour (for now) plugin instruments are fully associated with a single track. The best you could do is to create N MIDI tracks, 1 for each channel, without any instrument, and feed the output of all N tracks into a MIDI track with the multi-MIDI-channel plugin.
Alternatively you could change your working style and use an instance of fluidsynth per track. The cost of this should not be very much compared to the flow you’re used to; if it is then the plugin is oddly designed. Ardour is designed around this assumption. There’s no reason why running a N-voice synth or sample plugin should cost notably less than N instances of a 1 voice plugin.
Thanks for that, I’ll try the N MIDI tracks option, when I’ve learned about routing/busses! Unfortunately, even though I have a superfast computer with lots of memory, having more than one FluidSynth seems to crash Ardour, more often than not, so I dare not try it.