Ned if you can send me a small clip I would be gald to test it on my system.
Waveforms show flat. I can import other mono or stereo clips into PPro, allow the app to place them either in a mono or stereo track, and they then cam play. Only seems to be these Pix240 clips. And, as I said, these clips play fine in QT Player, FCP 7 and FCP X. Still have not tried MC 5.5
If I open the QT in Adobe Audition, there is audio (and of course, a waveform). Definitely something with how PPro is seeing these files.
Another testing update: No audio on my other system which is still at PPro 5.5.1. Audio is present in MediaComposer 5.5
I seem to be answering own questions. This solution is courtesy of a colleague writer.
Created a 4-track sequence in FCP 7 and exported that as self-contained movie. Brought that .mov into PPro. PPro saw 4 mono tracks and audio was present. Now PremierePro was unable to play the clip without stuttering and stalling so that raises another issue. Certainly the machine specs can handle ProRes HQ-- 8 core MacPro, 16gb RAM, Quadro 4000, ATTO R680 driving 8 drive miniSAS array, Kona 3G (latest 9.1 software for Kona and CS5.5 as well as latest Kona firmware).
Here's the answer after a day of research
The original Pix240 firmware did indeed have issues with CS 5.5. The 1.02 firmware which actually was the shipping version fixed the issue. PPro 5.5.2 broke the fix. SD is aware and the fix will be released in the next firmware update, which is "soon."
Thanks to all who contributed to the thread. I'l post when the fix is released.