Bad audio in Flash 8/VP6 using Flix
 

I'm at work in the middle of a major website overhaul - we're switching from offering all the trailers for our DVDs in both QuickTime (SV3) and WMV9 to Flash 8 with the On2 VP6 codec. I'm using On2's own Flix Standard to encode the trailers, and I'm impressed with the efficiency of the video codec, but the audio is quickly driving me insane. Flix introduces a ton of ugly artifacts and errors. The audio doesn't sound like it's clipping, but "ess" sounds become sibilant, I get a bunch of chime- and clink-type artifacts, and the dynamic range seems to disappear.

I've been encoding at the highest sample rate I had available (44.1 kHz), and I've tried a ton of bitrates. I finally settled on 40 kbps because it didn't seem to get any better above that, which seems outrageous. In the QuickTime trailers I make, I use AAC at 96 kbps in stereo, and it sounds fantastic. 96 kbps in stereo or mono in Flix sounds just as bad as 40, which is pretty bad. I've never liked the Windows Media audio codecs, but they perform much better than this using the same source material and similar bit rates.

Does anyone know how to get good audio out of Flix or at least out of Flash 8? I would be mildly ashamed to post this stuff on our site, even though the video looks good. I searched for examples of good audio in Flash 8 videos, and I couldn't find any. In the ones I've viewed, the video looked great, but the sound was either mediocre/poor or contained only music.

The two approaches I've tried so far were:
1. Increasing the bit rate. This didn't help at all with the sibilant sounds or the artifacts.
2. Converting my audio to 44.1 before running it through the encoder. This made zero difference.

I would appreciate any suggestions.

Flix uses MP3 as its audio codec, right?

I don't know much about it, but I can take a look if you upload a snippet.