Does some sums for less sensitive champs (6,8)

I believe the answer is:

number crunches

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'champs' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.

'does some sums for less sensitive' is the wordplay.
'does some sums' becomes 'crunches' (I am not sure about this - if you are sure you should believe this answer much more).
'for' means one lot of letters go next to another (I've seen this in other clues).
'less sensitive' becomes 'number' (numb means insensitive or unfeeling).
'crunches' put after 'number' is 'NUMBER CRUNCHES'.

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I've seen this clue in the Sydney Morning Herald.

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