I'm a little confused by the premise of your question.

Do you want to record a live track in one pass for both the guitar and vocals simultaniously?

If that is the case, you will need to have two tracks assigned in Studio One, one for the guitar (lets call this track 1) and one for the vocals (lets call this track 2).

In each track, select the input by pulling down the bar at the top left of each track next to the track info in your track window. Assign track 1 (guitar track) to receive the input from channel 1 of your audiobox and assign track 2 (vocal track) to receive the input of channel 2 of your audiobox. That way, each track will only record the input of each channel assigned coming from your audiobox without bleeding into each other. You can set each track to record in either stereo or mono if you wish.

You will need to have both record buttons on each track assigned to record at the top of each track in your track window (they will glow bright red when in record mode) and then use the bottom record button to kick off the recording when you are ready to roll. If you want to monitor both tracks simultaniously while recording, make sure the monitor button is assigned or on for both tracks, (they will be a bright blue when on...next to the record button for each track and usually come on anyway when you hit the record button, but can be manually turned off/on) that way you will hear what is going into your audiobox and is actually being recorded in real time.

This will give you better control over the mix where you can adjust the level of each recorded track, assign effects or plug-ins and the like to each track individually post recording.

IMO this would be the approach I would take as it gives you better control over the recorded tracks as opposed to having a single track recording in your DAW from both channels 1/2 of the audiobox, where the only control over the levels of your vocal and guitar is set at the audiobox before you hit record and cannot be varied or changed once its recorded as an individual track.
Doing it this way with two tracks each assigned to correspond to the two channels of the audiobox gives you a lot more freedom and choice to improve things after you have recorded the tracks to Studio One.

Hope this helps.

- Sean.