Simplify the following text for a Grade 6 native English-speaking person.
Original: Stokowski had previously given the US premieres of Shostakovich 's 1st , 3rd and 6th Symphonies in Philadelphia , and in December 1941 urged NBC to obtain the score of the 7th as he wanted to conduct its premiere as well . But Toscanini coveted this for himself and there were a number of remarkable letters between the two conductors ( reproduced by Harvey Sachs in his biography ) before Stokowski agreed to let Toscanini have the privilege of conducting the first performance .
Simplified: At first Stokowski wanted to conduct it but then he agreed that Toscanini would .