At first, it’s hard to think about anything besides those stairs.

Spanning four flights over three generous stories, the double-helix staircase at POST Houston’s retail atrium utterly dominates its space. Looking up, it resembles one X on top of another. Its gold railings, wide marble steps and green accents feel like something out of M.C. Escher’s imagination, maybe a vintage Gene Kelly production number.

It’s true, “chamber music” may not immediately spring to mind when considering Lovett Commercial’s mixed-use makeover of the former Barbara Jordan Post Office, slated to officially open in a few weeks. But ROCO has a knack for well-curated concerts in unorthodox locales, and parking a string quartet at the foot of those monumental stairs certainly qualifies.

The atrium’s tenants haven’t quite moved in yet, which Saturday night left the space feeling especially raw for Mixed Messages, the season opener of ROCO’s Connections series. The innovative local chamber orchestra and Houston Contemporary Dance Company, the concert’s co-producers, made this cavernous stretch of concrete, glass walls and HVAC ducts hum with creative energy. Surprisingly enough, the acoustics carried just fine.

It was also World Post Day, a chance to reflect on the lost art of letter writing. The centerpiece of the hourlong program was Elvis Costello’s “The Juliet Letters,” his 1993 pop/classical collaboration with the UK-based Brodsky Quartet. That project germinated after the “Watching the Detectives” singer saw Brodsky perform a complete cycle of Dmitri Shostakovich’s string quartets.

For ROCO, always making connections, that meant Mixed Messages opened with two movements from Shostakovich’s String Quartet No. 1. The ROCO String Quartet — concertmaster Scott St. John, violinist Ben Grube, violist Rainel Joubert and cellist Shino Hayashi — opened with a haunting melody that slowly spread from viola to violins, exuding an almost mystical calm. Darkening harmonies created a brief moment of tension, before a brighter section restored a deep-seated feeling of peace. The second movement found the players exploring a vibrant theme over Hayashi’s sturdy backbone until a dramatic finish.

Next, guest performer Outspoken Bean descended the stairs from the top floor, near the entrance to the 5-acre Skylawn rooftop garden. Opening with a good-natured riff on “On the Road Again” by Texas icon Willie Nelson — who christens POST Houston’s 5,000-seat 713 Music Hall on Nov. 17 — Houston’s poet laureate delivered memorable lines (“broken crayons color outside the lines”), rapid-fire retail jargon and some potent thoughts on identity, love and the power of “regular people.”

According to Costello’s liner notes, the vignettes of “The Juliet Letters” were inspired by a man in Verona, Italy, who took it upon himself to answer letters addressed to Shakespeare’s ill-fated romantic heroine. Costello’s febrile imagination did the rest. Saturday, the ROCO strings and Panamanin-born tenor Eduardo Alberto Tercero brought these letters to life, with no small amount of brooding and pathos. Although his vocals tended to sweeten Costello’s snider moments, the singer also channeled moments of real anguish.

As choreographed by Houston Contemporary Dance Company founder Marlana Doyle, roughly two dozen dancers filled the atrium’s stairs with white-clad bodies, sometimes swaying, sometimes standing stock-still, and sometimes sitting down and tossing crumpled-up papers onto the floor. Often they scanned the area, as if searching for something, or someone.

Using the stairs as a sort of vertical stage, they lent a distinctly dreamlike feeling to the performance, amplifying the evening’s themes of communication and miscommunication — by embracing and pulling away, for example — through purposeful movements and rough-hewn grace.