R600 won't exactly compete with the X-Fi audio processors from Creative labs. It will have an audio processing part, but this one will concentrate on High definition video.
Radeon X2900 has a UVD, Dedicated Universal Video Decoder part of the chip, dedicated for Video only. The decoder supports Blu-ray and HD-DVD, but it really doesn't care about the format as the UVD processes H.264 content regardless of the format.
R600 has a Xilleon video processor inside and this video decoder is an all-in-one integrated solution.
Integrated stand alone sound supports HDCP and HDMI and works well under Vista. It supports full HD sound. As far as we know today, R600 sound will be related to Video but there is a chance that you will have an R600 audio driver that will play your MP3's. We will try to get this for you.