He meant Multi-Boot GCOS discs...because they hold over more than 1.46gb they only work on wii...
I'm not sure why it doesn't work for you test. It should work fine, a lot of people use GCOS for this exact reason. (multi-disc games on one dvd5) have you googled around for some tutorials to see if there is something you could possibly try differently maybe?
You can fit 3 or so games in 1.4 GB.
Also, the Drive in the gamecube can read upto about 2 GB on DVD5 discs. Try it in GC-Linux.
You can't shrink all games, though. And like you said you have to mod the GC to linux to get it to even read up to 2gb.