I have PP CS5 5.0.3 and a Panasonic TM700 in 1080/50P mode, audio tracks are playable in the sequence monitor and when I edit a clip and drop it into the time line there is no audio in the time line at all. I have set up a custom preset in desktop mode and set it to 1080 50 progressive and to 5.1 sound. etc and saved it as TM700 preset.
This has been frustrating me no end as you can apparently edit these files natively in PP CS5
Have you tried dragging some footage onto the new item folder (next to the dustbin) in the project panel to create a new sequence?
This will setup a new seqence with the sound track that the clip is using.
A good place to start.
I have the TM700 and use it with CS5 PP all the time @1080/50p