In context that he was a founder-member, 'played with' is fine to mean he was still a member: if wished you could clarify by saying 'he continued to play with them...' but it would be a bit long-winded. The second 'Melos' bluelink is entirely optional: the article isn't long enough to make it really necessary, but repeat bluelinks from the intro paragraph into the main text are not uncommon and do sometimes help. I can't decide if 'premiere' for the Britten works should be singular or plural. A footnote source for the appointments at Michigan would help, as this is told 'on trust'.If there is more to add, it would be nice to draw the sentences together a little more into two or three paragraphs. But these are minutiae, quite at your discretion....! - all is well.