Ensemble Dialoghi makes their harmonia mundi début with this program of quintets for piano and winds. A work of 'maturity,' which the twenty-eight year-old Mozart considered ''among his best,'' is paired with a 'youthful effort' penned by a twenty-six year-old Beethoven. Dating from an auspicious phase in each composer's career, both pieces were met with an enthusiastic reception. Beethoven, it was said, was inspired by Mozart's piece and composed his in tribute. The theatrical character of these works is not lost on the high-spirited virtuosos who make up this period-instrument ensemble.