Well, the bad news is the 990 won't support any of the high res sound formats you listed. But then, neither will the optical link in either bitstream or PCM.

So I would suggest putting the Panasonic in Bitstream, change the Downmix to 5.1 and put the 990 in Dolby Digital mode. If it's like my Panasonic this should put everything in Dolby Digital 5.1 format. (Note: DTS would require the 990 to decode DTS)

Otherwise try PCM (which is 2-channel output) with the 990 in PL II Movie mode (Pro Logic 2).

I believe the 990, like my 970, will automatically try to match it's setting to the input so once you get the Panny set up the 990 should just work.

Be ready for MAJOR improvment when you get HDMI support and can get full high def sound. For now you're stuck with plain old Dolby Digital or DTS. (Although the 990 could matrix up to 7.1 using PL IIx.)