Don’t lump the San Diego Symphony in with all those North American orchestras struggling to make ends meet. The ensemble, which recently received an unprecedented $120 million gift from a local couple, is flush with cash, and the financial security is starting to translate into measurable artistic gains as well. The average musician’s salary will jump $14,600 this season, and the marketing budget has tripled. A $3 million office renovation has been completed, and the SDSO ended the 2003 fiscal year with a $600,000 surplus. So what’s next? More fundraising, of course.