I'm also curious about such things. It would be interesting to know why emulation so significantly slows down running on Windows even on the most powerful of PCs when the GC is only composed of a 485 MHz processor and 43 MB RAM.
A emulator is just a "translator"...
It translates CPU language a to b and thats not easy!
Its like you get a word and think a moment what it means and translate it to the correct meaning.
One might think of this way...
In the low level workings of hardware, you just don't tell your sound card to play song X, but you feed it constantly with audio information. The same could probably but said about emulators. It needs to fetch audio data in pieces and play it. When you get below "real speed", the emulator just can't get enough pieces quickly enough to be no "hickups."
And a other problem from the emulation of Gamecube sound is that the audiohardware isnt well documented... Dev´s really try hard to find a way to get gamecube sound work more reliable but they unfortunalty cant...