Hi Mark,
Yep! You can do that. The internal SD card recording system is independent of the USB audio interface function.
Just set up the SD Card recording as you normally would and set up Studio One for multi-track recording. You may have to choose from the mixer, which Capture device the mixer's transport control buttons are addressing. I believe they can control either the SD card recording system or Studio One. I believe you can choose whether the mixer's transport buttons address the SD card recorder or the DAW via the UC Net button (below the main screen of the mixer).
Otherwise, just hit record on both the mixer and Studio One.
