Not quite sure how it works on a 16R (never tried) and I don't have the mixer here at the moment, so I need to guess. Probably Capture shows up in UC Surface when you insert a SD card. Not sure if you need to load the mix scene - if there is any. The SD recorder sends its signal to "Tape In" (also called "Digital Input"), which you should find after the FX returns and Aux In's. Select this stereo channel and choose SD as input source.