Realistically, if you can't open up a new USB input via whatever gizmos you could find on amazon, you could simple bung in a MIDI cable and send that from the keyboard to the interface - which will then appear in your DAW as a MIDI source. Options then would be to use a nice VSTi for a piano sound. To be honest, yamaha electric pianos, since Clavinovas were first around, sound pretty nice through their internal speakers, but are always a bit less realistic if you take the audio from the yamaha and stuff that into your interface and record it. However, it will work as an audio source, and MIDI as an option gives you editing? Your call really. My choice would be 100% MIDI and a piano in the computer - which of course gives loads of options, the best of which is fixing bum notes without re-recording.
