Normally I wouldn't even use the Wii but since my friends got a complete set-up on it without just getting it on Xbox, I gotta figure out customs on the Wii in order to use their instruments when we all play.
Anyway, I made sure my Wii was softmodded. (As far as I'm concerned it's done right but I don't mainly use the Wii for this so I may have to look deeper into the potential issue there myself)
Sorry that this post is so long too, I just wanted to explain my process in detail just in case I'm doing something entirely wrong, but I tried following the guide.
Assuming it's modded correctly, I made sure I followed the difficult steps from converting an Xbox CON (specifically Master Of Puppets, not that it really matters I guess but why not say everything) to the "_meta" and "_song" folders with the Wii Converter option in C3 CON Tools. I changed the first three digits on the "_meta" folder to "052" and the "_song" folder to "053". The eight digits after the underscore for each are "00000034" and "00000035", respectively. I changed the indicated path in the songs.dta file to "dlc/sZFE/052/..." and dropped the two folders into the "sZGP" PAL DLC Packer folder. I used a real DLC ".bin" file to obtain the "ng_id.txt" file by putting it through the Wii Converter, and I was a bit confused on how to specifically get the "common-key" file working but I'm pretty sure it's right as well. One thing about the "ng_id.txt" file too is that it came from a single ".bin" file only, since I realized that they tend to come in twos, and it was from DLC I had purchased a long time ago on the Wii that had been saved there for years and never been used since. The songs themselves didn't seem like they were able to run properly because in RB3, they showed up with the grey Rock Band logo picture for the album art and a little SD card loading symbol. I'm not worried about those songs working though, just didn't know if that had anything to do with the "ng_id.txt" file being associated with them along with the fact that they don't seem to be working right.
After replacing the existing placeholder files in the "sZGP" folder, I ran "RB3WiiPackTool.exe" and ran the generated "packdlc.bat" file. "00000034.app", "00000035.app", "052.bin", and "053.bin" were all then born, and I copied the two ".bin" files alone to "...\private\wii\data\sZFE\" in my SD card (with all of the softmod files in it) and put it into the Wii. With this entire set-up specifically, I just got a form of corrupted file error and the files were deleted automatically. I tried a few other variations, such as throwing the "_meta" and "_song" folders along with the ".app" files into the same location on the SD card and of course nothing. I also was accidentally running the Wii Pack Tool with the default sample files since I didn't know what I was doing and only when I replaced them was when the Wii recognized the ".bin" files as corrupted.
One thing that I'm noticing too are all these folders starting with "sZ..", and the tutorial specifies using "sZFE" while the RB3 Wii Pack Tool uses "sZGP". Didn't know if that really mattered. Also the reason why I'm using the PAL one, "sZGP", is because the other, "sZGE", wouldn't create the ".bin" files. Might that be an issue?
I know I need to use ".bin" files too. From what I understood the ".app" files were specific to the NAND process, however I verified that for my own Wii's specifications since my existing DLC songs were actually in ".bin" format. Speaking in regards of the NAND process, it doesn't sound like something I'm using from how it's explained. Is it something I have to use too though?
I just don't know if maybe I could be doing something wrong in the Rock Band part of this process or if maybe this is an issue with the mod set-up. Like if there's a Wii version of a title update file I need or something like that. If it's a modded Wii problem, then I can figure this out elsewhere unless someone is willing to help me. Some other basic specs that I guess could also be essential is that I was seeing a lot that it's preferred that you have a SanDisk brand SD card for modding, and at the moment I just got some 4GB Kingston brand one. I also dunno if it's necessary to use a USB drive instead, if it'll load any better that way or something. Other than that, I'm using the EA Rock Band 3 disc, if that even matters in this process. I guess that's all I got to mention about this. I appreciate any help! All of this could have been avoided if my friends bought Xbox Rock Band stuff rather than Wii Rock Band stuff, so unless anyone knows how to use Wii instrument controllers on the Xbox 360, which of course I assume is impossible, then I gotta figure this out or just get bored of the on-disc songs all the time lol. Also I hope I didn't discuss anything I wasn't supposed to. This post wasn't intended to do that.