What you desire is currently
not possible. You need to use a regular Wii for 8 player support.
@wilm0x42 /
@Chadderz both have been developing some form of GCN adapter support.
@Peninsula and I tried to work on adding 8 player support for Bomberman Blast in April with no success. The only
potential solution at this time is using Chadderz brainslug module (linked below) with a Japanese imported Bomberman Blast disc (I think the game is just called "Bomberman" for the Wii). Unfortunately, I don't know anybody who owns the physical disc who can test out this theory.
Wilm's version works beautifully with Brawl/ProjectM with a physical disc. He was in the process of adding support for USB Loaders, but I think the project may have stalled. Regardless, his project is almost guaranteed to remain exclusive for Brawl/ProjectM (
https://github.com/wilm0x42/wii-gc-adapter-inject).
Chadderz's version works on multiple games across multiple regions, but requires a game available on a physical disc. I'm aware of an update to the public source, but he never got around to committing it. Last I heard, he still intends to commit the update to GitHub (
https://github.com/Chadderz121/wup-028-bslug). Chadderz's other project, CTGP requires a physical disc as an anti-piracy measure so my gut feeling is that all of his projects will never add support for ISOs/WiiWare/VirtualConsole. I believe he did state at some point the implementation has potential to work with a WAD if somebody skilled enough knows how to modify his source to access NAND instead of a disk.
Hope that summary helps! Please let us know if you are able to try the Japanese version of Bomberman!
Main discussion thread:
https://gbatemp.net/threads/need-help-with-vwii-gc-adapter-for-project-m.498236/page-12