Premiere version 4.2.1
Matrox Rtx2 version 126.96.36.199
Core 2 quad
Creative X-fi sound card set to Audio creation mode
Windows 7 ultimate 64
If I run Premiere with the ASIO drivers I get the 5.1 that I need but I find that premiere crashes when trying to play audio only clips, either wav or mp3. Often it just keeps playing and I have to do a ctl-alt-del to stop it. Also it won't play from the preview in the projects window. If I use the standard windows driver I loose the 5.1 function and about one time in ten playbacks the stereo channels are out of sync by a few miliseconds. I can well believe that it is the creative card that is at fault, does anybody have any recomendations for a better (but afordable) 5.1 sound card.
Many users have had issues with Audio and Matrox cards, so keep that in the back of your mind.
Now, can you get ASIO4ALL (freeware), install it, and point your Audio Hardware ASIO Settings to it? Do you now have better performance.
As for MP3's, I would strongly suggest that you convert these to PCM/WAV (Uncompressed) 48KHz 16-bit files. This will not recover all of the data lost in the MP3 conversion, but will give PrPro the best Assets to work with. MPEG Audio can really case issues, and MP3's carry some extra headaches. I will ONLY use them for tiny SFX files.
1. Matrox has an update driver 4.2.1 (build 171) for its card.
2. While I don't have your audio card, have no problems with MP3. Don't use dolby 5.1 much - can't help there.