i've been working on this off and on for several months and i've yet to been able to soft mod my wii to play gamecube backups. i have gotten wii backups to work, but whats that worth if i can't play LoZ Windwaker? i do own a gc controller and gc mem card if you're wondering. Will i require a modchip? i hope not.
Im not up to date on Nintendo modding but going back a few years ago i successfully modded mine and was playing gamecube backups without needing a chip, a softmod should do the trick. Maybe post the Wii model, FW, what softmods you have tried etc, this may help with the support process and get you support quicker from someone with knowledge on the topic. As i said i have not been into modding Nintendos for years, wish i could help
mabey this will help u http://digiex.net/guides-reviews/console-guides/13079-how-play-gamecube-backups-wii-via-sd-card.html