if an amsynth instance is being inserted as a LV2 plugin on a MIDI track, then you should access any of its parameters as from the "A" button drop-down menu, Select -> amSynth -> parameter...
which part do you miss there?
[UPDATE:] just figured out now that you're running amSynth as what i called a stand-alone instance, so definitely you'll need to go with option b) above and there try assigning a MIDI controller to the knobs or parameters in question and make the MIDI data to control them as part of the performance itself in the MIDI clip (in qtractor).
of course this option only works iif amSynth (or Catia) makes MIDI controller mapping available--also called "MIDI learn"--something that you'll have to ask to the amSynth/Catia authors if not readily from their manual docs:)
if an amsynth instance is being inserted as a LV2 plugin on a MIDI track, then you should access any of its parameters as from the "A" button drop-down menu, Select -> amSynth -> parameter...
which part do you miss there?
[UPDATE:] just figured out now that you're running amSynth as what i called a stand-alone instance, so definitely you'll need to go with option b) above and there try assigning a MIDI controller to the knobs or parameters in question and make the MIDI data to control them as part of the performance itself in the MIDI clip (in qtractor).
of course this option only works iif amSynth (or Catia) makes MIDI controller mapping available--also called "MIDI learn"--something that you'll have to ask to the amSynth/Catia authors if not readily from their manual docs:)
hth.
cheers