I think you need a SOS for each box, with values 1 to 24 (7+8+9) since you could have just 1 cell in the box, value 1, or at most 3 cells with total 24.
Then apply the standard log trick. ie. 3 = log(1) SOS[1] + log(2) SOS[2] ... + log(n) SOS[n] ... + log(24) SOS[24]
https://app.crackingthecryptic.com/sudoku/Tgb6g6rPR7
Clues outside the grid give the multiplication of the boxes sums that the diagonal passes through.
e.g the 1000 clue on the SW-NE diagonal means the that
(R1C9 + R2C8 + R3C7) (R4C6 + R5C5 + R6C4) (R7C3 + R8C2 + R9C1) = 1000
I think you need a SOS for each box, with values 1 to 24 (7+8+9) since you could have just 1 cell in the box, value 1, or at most 3 cells with total 24.
Then apply the standard log trick. ie. 3 = log(1) SOS[1] + log(2) SOS[2] ... + log(n) SOS[n] ... + log(24) SOS[24]