According to the following article, the audio change happened for most GC games in 3.5-78, with Wii games happening later in 3.5-1154: https://dolphin-emu.org/blog/2014/11/12/the-rise-of-hle-audio/
As for the OpenGL improvement... Hmm, I haven't been keeping that much of an eye on the graphics side of things, so I'm not sure what it is. It sounds unlikely that it was added earlier than the versions I mentioned above, though.
As for the OpenGL improvement... Hmm, I haven't been keeping that much of an eye on the graphics side of things, so I'm not sure what it is. It sounds unlikely that it was added earlier than the versions I mentioned above, though.