"My question its : audiobox will send them as separate channels to Studio One ?"
Yes, as long as the iOne reads the Mic and Inst inputs as separate channels, which I'd assume it does !
Considering it does, then you'd want to add a Stereo Input in the I/O settings in Preferences, and create a New Stereo Track with the Stereo Input.
Of course you will have to gain stage your two very different inputs to a nice balance, so make sure you enable Input Controls and watch your Input Meters in the Console very carefully.
You can also do it your way, hard-panning the Mic input Left and Instrument input Right, and then mixing/mastering and exporting a stereo mixdown. Again , all this assumes that the Mic and Inst. are considered 2 separate inputs in I/O setup !
Best of luck, lemme know how it goes !