Only thing is, I can't get it to trigger note-ons (tested in Psycle). I think it's because I'm missing a module or two mentioned in the tutorial, but I'll check it out again.
Hmmm...I don't get what you mean. You enter notes and it doesn't make a sound? Maybe the patch you did doesn't have MIDI in.
No, it always makes sound the instant the plugin loads, but it doesn't react to note-ons. I'll update to a new version of SynthEdit, anyway.
A "note on" happens when, during playback, the playing bar passes over a note, right? For example: "C-5 00000". Maybe Psycle is buggy. Have you tried in Renoise?
I know what a note-on is, dang it

. If it's Psycle, then why do other SynthEdit synths work? I'm just missing a module...
I know you know what a note on is. I was just making sure *I* knew

Have you checked if the synth that doesn't work has an "IO Mod"? That's necessary to receive MIDI signals.
EDIT: Acutally, two "IO Mod" units are needed. One for "in" and one for "out".