To the best of my knowledge, this is a rather unusual microphone technique for piano. Two figure-8 ribbon mics are placed equidistant from the center of the piano – one facing down from above and the other facing across the strings from the side. Mics are panned hard left and right, and because the figure-8 patterns are picking up and rejecting in opposite planes from each other the result is a very spacious stereo image. The lid must be removed for this to work well. To hear another example of this technique, listen to Todd E. Hill on iTunes.