Okay I'm starting with I know Bizhawk is younger than Dolphin so don't snap crazy.
Anyways, Dolphin emulator is young there isn't many people behind in developing this you chose Mario Bros. Wii and let me be frank, Wii games have a shit ton of desync, so you must go through find that desync and continue from that point.
It's long and tedious and how new this generation is (5ish years) it is surprising that Dolphin tas emulator is better than the Playstation 2 one (and
mupen). So in all Honesty there is no point of doing bizhawk Wii at all, seriously all you need is patience. Gamecube tasses fine on Dolphin because of tas input, all the Wii part of it needs a tas input and it would be set great.
If that's not the angle you want don't throw a
tantrum at me (it's a good drink (sarcasm as it doesn't exist... I wish it did though :/)).