possibly. i'll tackle that later.
sadly, it's like what you saw. there's no good resources.
i brute forced my way into it and figured how to run it by trial and error.
i can give you some instructions so you at least know the general directions instead of aimlessly trying things.
instructions to get GBI running:
first, you need a way to run homebrew on GC. there's many ways depending on what you own.
method 1: a hard mod. this basically means your GC is hardmodded to run copied discs. burning the swiss and GBI files to it and then loading the disc lets you run them (i haven't used this so i dunno if there's extra steps)
method 2: a SD media launcher. for this, you buy a SD media launcher that comes with an Action Replay disc. the SDML is an adapter that lets you plug an SD card to a GC memory card slot. you put files in the SD card and when you load the AR disc, a menu pops up and you start the app you want. there's also a way to build your own adapter if you can't find the SDML adapter but you'd still need software capable of handling it.
method 3: using a hacked savegame installed to a GC Memory card using Wii homebrew. this method has become more viable lately since there's a couple of games whose saves can be hacked. games that work include SSBM, TWW, TP and the Pokemon Colosseum/XD games. this is useful if you already have a Wii since you don't need any additional hardware, except for one of the games and a GC memory card. loading the homebrew files depends on the game but it's simple most of the time (go to one specific place or menu and the hack triggers)
after you have the ability to run homebrew through any of the 3 methods, the first program you run is Swiss. this program lets you configure the output resolution and other things before loading an app. this also lets you set the options for the regular GBI app (LL and ULL can't be customized. the customization introduces lag due to the framebuffer needed and these versions' purpose is to reduce lag)
after that, you run GBI and are ready to play your GBA games on TV. the latest GBI supports GBA as a controller on controller port 2.
the GC forever forums has threads with the required files. you can find GBI and the softmods needed to run it.