I, too, have the Hans-Hubert Schönzeler Bruckner, Grossman Publishers, New York, 1970. Read it years ago at which time it seemed to cover all the bases adequately. I agree that AB's life—as opposed to his music—was not all that interesting.
I have two other books which I would recommend ahead of the Schönzeler, though both appear to be OOP:
Bruckner, Derek Watson, Oxford University Press, 1975/1996
Bruckner Remembered, Ed. Stephen Johnson, Faber & Faber, 2001
The Watson contains some musical analysis as well as a biography, and the Johnson is, as the title suggests, a collection of reminiscences.
James