The Detector input is for inputting a clean signal into the pedal for optimum note tracking. You can use a splitter cable from your guitar to send one output to the harmonist and the other to the rest of the pedals in your chain.
Keep the HR-2 first in the chain, perhaps a compressor or light overdrive/booster before. The detector works so so. A y-chord isn�t a good idea (I have tried it), it should be something like an "electronic" splitter if I understand the manual.
i love mine, best to use a small junction box, with an input and multi outputs. It works a treat. Must keep guitar in tune and do not play chords, they dont come out so well
I use either my LS-2 or SYB-3 to split my signal, depending on what I'm doing. Having clean input to the detector makes a huge difference when running distortion in front of the HR-2.