Hello HD ,
today the same problems again ,no audio trough HDMI, and now I let the mede8er play and while playing I changed the HDMI cable with a new one ,first in front HDMI from the Panasonic plasma screen and voila sound, then the new cable in the old HDMI port also sound, then I put the old HDMI cable to the Panasonic, no sound. So all the sound problems came from the old HDMI cable.
I also have a quicker initialisation when I choose the HDMI port on the Panasonic with the new cable.

So HD, you can always try this because I had the same problems as you, first always sound,with firmwarew 304, then firmware to Version 4, after a while no audio trough HDMI ,back to 304 ,no audio trough HDMI, new cable n0 plroblems!
Analog always sound! So buy a new cable HDMI 1.3.
Kindly regards Richard!