Isn't it likely that whoever created the existing recording just plugged their Wii sound output into their PC's soundcard?
I've ruled out that possibility based on a number of reasons. The hierarchy of the current rip looks too broken down and "organized" to be just a recording. The sheer number of tracks, short as many of them are, strongly indicates that it was a straight rip, and not a direct recording of the suite-based sound test in the game itself. On top of which, the files are still originally labeled as .brstm (for instance "BGM 001.brstm.mp3", "BGM 002.brstm.mp3", etc), an apparent sound data extension designated specifically for Gamecube and Wii games.
More evidence is that the in-game sound test has the unfortunate habit of stream-playing its songs off the disc, yet does so by beginning or ending many tracks prematurely. This was proven not just from myself, but a few others who had attempted to make a direct recording. In other words, a rip appears to be the only way to get the fully played renditions.
In any case, rips are certainly possible. I mean, look at those massive Super Smash Bros. Brawl music projects that are available.