There's only one instance of there being streamed music in the DS Pokémon games and it's the B2/W2 title screen.
You'll have to use midis for anything else as mentioned above. I don't know if you could sample a whole song in PCM as people have done with the GBA games.
I believe you're quoting the wrong person. There's a thread on GBATemp under 3DS ROM Hacking by Asia81 with shared textures, including those you mentioned. Yes, they're texture edits, not model edits.