"I’m a lifelong student,” Bruce Hornsby says. “I’m always trying to push what I do into new, exciting vistas, and make a sound I haven’t heard before. That’s the challenge, for me.” The piano man, today wearing jeans and a blue crew-neck shirt, talking to Classic Rock at his at home in Virginia, is an expressive conversationalist, speaking in long, complete sentences that are often punctuated by side notes and bursts of easy laughter. He’s not k…