User blog comment:AtomixGirl/Why digit and tune were switched/@comment-33016172-20170902221037/@comment-31892545-20170902221527

Michal Friedman was Tune's 4Kids voice actor. When Digit and Tune were switched, Nick was dubbing and coproducing Winx Club, and Tune's Nick Special-S4 voice actress was fine. They swapped the original Nick pixie's voices in S6 for their bonded fairies' voices, I presume because of budget cuts. Even so, Winx is no stranger to replacing voice actors, so I don't think this would've even been a case.