Since his debut release on Mack Avenue Records in 2013, pianist-composer Aaron Diehl has mystified listeners with his layered artistry. He reaches into expansion. At once temporal and ethereal — deliberate in touch and texture — his expression transforms the piano into an orchestral vessel in the spirit of beloved predecessors Ahmad Jamal, Erroll Garner, Art Tatum and Jelly Roll Morton. Moment to moment, he considers what instrument he’s moved to evoke. “This is a singular voice here, but maybe this section is a saxophone soli, or this piece here are high winds or low brass in the bass,” says the Steinway artist, describing his concept on the bandstand.