There is a seriously easy way to do this in Cubase/Nuendo.
If you need a dry signal down one side and the amp down another, simply change the plugin from default stereo to mono in the Cubase routing controls (where it is saying "stereo" in a sort of blue button - I would post a screenshot but amm exporting a mixdown right now so cannot access it), and then open the routing editor to select what side - left or right - you need Helix to be operating on.
Job Done, and no messing with Y-Splits or any of that as you are guaranteed a mono signal path.
