Albert Barnes Commentary 1 Chronicles 9:9

"and their brethren, according to their generations, nine hundred and fifty and six. All these men were heads of fathers` [houses] by their fathers` houses." — 1 Chronicles 9:9 (ASV)

The discrepancy between the numbers here and in Nehemiah 11:8 may arise from a corruption of the text, as is also the case in 1 Chronicles 9:13 and 1 Chronicles 9:22.