Can you open the arc files in a hex editor and post the header letters? (meaning the first four or more letters in the file). Or by using notepad. I don't think the wii files are Yaz0r encrypted.
I'm new to Nintendo files but I thought Yaz0 was compression? It looks like a RLE compression. Yes Wii games still use it. The .carc archives of Wii Sports are "compressed" arc's and decompress fine. Mario Kart .szs are also Yaz0 compressed.
Oh and I registered to ask if anyone has listened to the audio tracks on Mario Kart Wii. The sounds look to be stored in brsar's, just an archive so extraction would be easy. The actual audio have a "RWAV" tag in the header. Any info on this? It is structured like a .wav file but no luck outright.