Emmylou Harris is a consummate professional and her shows over the course of 40 years are remarkably consistent. The set list is always a careful mix of tracks from her entire recording career with a mid-show emphasis on her new album. There’s some thoughtful, informative presentation and background, an occasional story and the band introductions. The musicianship is impeccable bolstered by occasional dancing. There is usually some fringe clothing. Her hair is perfect. She has a pure voice that always points to the transcendent and she has compensated well for the invariable changes that come as the years go passing by. She occasionally tours with a co-star, and last night at her XRT show at Symphony Center it was singer-songwriter Rodney Crowell, one of her musical muses from the very beginning. He was also a former member of the greatest incarnation of the legendary Hot Band. Despite an unusual technical glitch at the very start of the show which spawned some Grand Ole Opry style mildly salacious repartee, everything went smoothly thereafter. There was a generous amount of tunes from their new collaboration Old Yellow Moon along with old favorites like “Till I Gain Control Again”, “Wheels” and “Love Hurts”. The co-headliner was Richard Thompson, touring on the strength of his fine new album Electric with a drummer and a bassist. They opened with selections from that disc and peppered it with some catalog choices like “Tear Stained Letter” and a blazing acoustic take on the greatest motorcycle song ever written “1952 Vincent Black Lightning”. Thompson was already a guitar virtuoso back in the 60s in his stint with Fairport Convention and he continues to get better. You’d have to call him a rocker, but his style is informed by Celtic reels and fiddle tunes played almost always in a mournful, wailing minor key. At breakneck speed. He joined in with Emmylou and Rodney on “Ain’t Living Long Like This” but let the young hot shot in the headliner combo do most of the work, just like a polite, invited guest would do. Nonetheless, it was certainly one of the best guitar duels ever heard at Orchestra Hall. Everyone went home happy.