The thing that worries me is that, deprived of the audio input, the harmonizer didn’t really work at all well. It ought to work pretty well without the audio, maybe not as good as both (I’m not really familiar with your particular TC, is there anything in the manual that cautions against using only MIDI..?) and if it isn’t, it seems to me that something is out of whack…

Mind you, if your current setup works, it works! I’d still try using a send from the mixer to get both sides of the arranger to your speakers in future, though…