Can you elaborate why you need an audio cord from the arranger into the TC unit?

Doesn’t the MIDI (or USB cord) send whatever harmony information the pitch transposition needs?

And yeah, sadly, compared to pro units designed specifically to impress singers, there really isn’t a single arranger manufacturer that makes a standalone vocal harmonizer that is as well regarded as TC. I always feel that, if a company doesn’t make a great anything (harmonizer, vocorder, Hammond clone, whatever) in standalone format, it’s not going to have the code and chips to put one in an arranger…