It's interesting reading the documents too, that apparently the SNES instruments were actually already inside the rom but were unused and just swapped out with 8bit samples instead.
Indeed, but it's not 8-bit samples (all GBA samples are always 8-bit), but GameBoyColor audio used. In addition to Direct Sound, games tend to use Game Boy Color audio for some reason, even though it would be largely unneeded in most cases.
Apparently Capcom arbitrairly limited themselves to 2 simultaneous Direct Sound samples in Breath of Fire I and 3 samples for Breath of Fire II, leaving the rest to GameBoyColor audio or just dropping tracks. This was largely un-necessary, as having all 8 tracks in Direct Sound works after hacking the IRQ routine a little.
Also makes me wonder whether Capcom's other GBA ports (like the Disney Magical Quest trilogy) also have the original music samples contained as well.
I don't know Disney Magical Quest so I can't answer, but I can assert Mega Man & Bass doesn't have them.
It has been a lot of fun witnessing Bregalad demonstrating such an incredible job accurately replicating SPC700 on GBA, and in such high quality. GBA was always shat on by gamers as inferior and incapable of doing this.
Yeah, the GBA can do it just fine technically, even if it requires sometimes throwing some CPU time at the task. Which apparently many developers were afraid of.
Makes you wonder if MMBN's sound team had any work in this porting though, since the games had a good share of a sort of 8-bit.
I don't know, but MMBN makes a much, much better usage of GameBoyColor sound. Actually it's probably some of the GBA games that uses it the best in my opinion.