I thought if there is any difference it should be in the audio not video.
The Panasonic website gives the following differences between the 320 and 500:
S/N: 105db 100db
Dynamic Range: 105db 100db
I don't know if these differences are for Analog or for both digital and analog?
I am also not sure if there is any difference in picture quality between the two because the Panasonic website gives both units the same thechnology for picture quality.