When Edo deWaart took up the reins of the Sydney Symphony Orchestra in 1993, he was exhausted, drained by the various stresses of leading orchestras in the dual pressure cookers of Europe and America. This week is deWaart’s last in Australia, and as he prepares to take over as music director in Hong Kong, he refers to Sydney as his “spiritual holiday.” During his tenure, the SSO significantly improved its musicians’ wages and working conditions, and critics say that the orchestra is a decidedly better ensemble than it was when he arrived.