I've never tried it before but I've got the Creative SB Audigy 2 ZS 7.1 Platinum Pro with the Gigaworks 750 7.1 speakers (both THX-certified) and a DVD drive.
I went down to Virgin yesterday to buy some DVDs and picked a copy of The Eagles - Hotel California on DVD Audio.
I played the first track (Hotel California) and my jaw dropped on the floor!
I have
never heard such quality in my life!
For those who don't know, DVD Audio is played back over 5.1 channels (upmixed to 7.1 on my system) and is 24bit/96Khz quality - loads of headroom etc.
The discs also have usual Dolby Digital 5.1 and DTS soundtracks included as well but as these are compressed and are only 16bit/48Khz, they don't sound as good as the DVDA part.
Highly recommended, my next purchase is going to be Tubular Bells from Amazon.