Most conductors are musicians first, of course, but it is fairly rare for a great conductor to begin his career as a great orchestral musician. (This may have something to do with orchestral musicians’ well-known hatred of most conductors.) But when the Chamber Orchestra of Europe celebrates its 25th anniversary next week, the man on the podium will be Scotsman Douglas Boyd, who rose to prominence as the COE’s star oboist, and who has since crafted an unlikely second career as a highly regarded stick-waver.