17, 20 and 22 across are beyond me. They are (in order) E 1? (6); O 1? (8); N 1? (6). The only other clue (given at the top of the crossword) is 17, 20 and 22 across refer to the same person.
I thought the E, O and N came from the positions of the letters in his name BE(E)TH(O)VE(N) refering to the 3rd, 6th and 9th symphonies. ie eroica, pastoral and choral