I've used a bunch of microATX nForce boards, and the audio on all of them has been perfectly fine for me. I play a lot of games, MP3s, etc. If your brother is doing any high-end audio editing, then maybe he needs something like an Audigy. But if he is anything like me, almost any nForce2 board will work fine.
I am currently most fond of the Biostar M7NCG 400 board. I've used the Shuttle MN31/n, but have had problems, I think it's because of the power supplies I used.
Also, be aware that you should use dual channel ram if you want to use the onboard video.
EDIT: The Shuttle also has dual vga ports, which is really nice if he wants dual monitors without having to get a second video card.
