This tutorial is not outdated in the slightest. The information this tutorial provides is still relevant, as there hasn't been any further documentation on this sort of SFX editing via PSA editing.
If neither BrawlBox nor Tabuu work for you, then you're forced to manually hex edit.
If you can't get anything to work, it's likely not the fault of the tutorial, but rather yourself.
Though not to mention, Smash Boy already figured out their issue over Discord.
Well, I never said it was the tutorial's fault. But it is also definatelly not the user's fault neither.
Good he was able to solve his issue.
But to be honest, there should be a Hex tutorial for this or at least an update to PSA so these SFX IDs can be modified too.
IDK if there is already an update to it since it's been quite a while since I stopped modding Brawl.