Oh yes, for some reason I forgot to tell you - I was really tired when I sent you that last PM. I really had no clue what the hell I was thinking then XD Don't worry, I understand the Tutorial just fine, and I got it to work right on my first go.
Anyways...
Well, you can't change an actual wav file's volume without using Wav editing software, but yes, there is a way to change volume.
For example, I'm assuming you're using a clean Ruby rom.
Open up sappy, and load the song. For this simple tutorial, I'll be using the Regi Battle Song. Let's say that I want the first instrument to be super loud. What I would do is press play, then press stop right after that. I'll not only get the offsets to the individual tracks (which you already know), but I'll get a bunch of other junk too.
Some things you will see:
Rel - I'm not entirely sure what this is.
Len - Length of the note.
Note - Note number/value
Velocity - Not entirely sure what this is either.
? - Well, nobody really knows. Maybe just a buffer.
Mod - Modulation, it's used in many Golden Sun's songs, but far less often in Pokemon's. This affects how the song sounds. Invalid modulations produced by Sappy's "export Midi" command crash Sappy.
Pitch - Used in pitch bends, such as in Magma Rock (I think it's used in Fog of Mt. Pyre but I'm not certain)
Pan - Pan is whether you hear the song from the left speaker or the right.
Now here comes the important parts:
Voic - Voice number. Same as midi number minus 1. For example, Lead 1 (Square) is Midi number 81, but in Sappy, it displays 80 (this is because midi numbers usually start at 1, but Sappy and the GBA's music system begin at 0).
Vol - This is what you're looking for. This is the volume for a track. For the first track of the song mentioned above, it says the volume is 80 (Hex 50).
So we go to our first track, which is located at 0x86ACA58. Here we see:
BC00 BB50
BD30 BE50
BF40 D749
Now, the italicized part is the instrument number. Yes, you can change instruments a lot easier now!
The bold part is where most likely our volume is located.
The underlined part should NEVER be changed.
Now, I change the bolded place to 0x7F. This is the loudest a track can be. Now the track is much louder than the other tracks. Changing it to 0x01 is the quietest you can make it, so, if trying to make a track quiet, try going with a lower hex number than the rest of the tracks.
By the way, it should be noted that this works only most of the time. If the volume doesn't change, it might be that Sappy messed up on finding the volume of the song. Look for it byte by byte then (it's a real pain but it shouldn't be far from where I pointed out).
Hope this helps.