Not trying to be condescending, but your buddy might not understand how marginal tax rates work.

  taxB > taxA

  $salary * (1 - taxA) = take-homeA

  $salary * (1 - taxA) + $raise * (1 - taxB) = take-homeB

  take-homeB > take-homeA

In short, if his wife earns more, only the new, additional income is taxed at a higher rate.