Set up the stereo piano in the live room. Connect it to the mixing desk. Use a splitter cable to connect to two separate channels, if necessary; some keyboards have a single, stereo output while others have two separate outputs.
Put on headphones ("cans") with volume control in the control room and have an assistant in the live room put on headphones too. Turn the volume control on your headphones to low to protect your hearing during the volume check and have your assistant do the same. Turn the volume up gradually to a comfortable level.
Ask your assistant to play as loud as possible (indicated by "fff" in written music). Move the volume sliders on the mixing desk until the sound is peaking at the upper limits. Ask your assistant to play as soft as possible (indicated by "ppp" in written music). Move the volume sliders on the mixing desk until the sound is just audible at the lower limits.
Use the pan pot to send different amounts of input to different channels. Adjust the pan settings on the two channels to replicate the authentic sound of a piano, i.e., lower notes to the left and higher notes to the right (but not extreme left and right). Set EQ controls to zero for recording purposes to allow bass or treble frequencies to be adjusted more dynamically during mixdown, when pan settings can be changed too.
Start the recording session proper, secure in the knowledge that the stereo piano sounds authentic, that pan settings are appropriate and that every note played will be captured. Cover any playing mistakes by punching in replayed sections. Discuss EQ settings with the pianist during mixdown.