I think I know the reason why it does not work but is there a workaround. The front stereo speakers are bi -amped using channel 6 and 7. This has the effect of preventing these channels from being configured in the menu, which is why I think that some DTS disks will not have any sound in 5.1 mode. If I change to stereo downmix or mono the sound returns. This only happens on some DTS disks such as LOTR TWO TOWERS or FINDING NEMO. THE DAY AFTER TOMORROW plays the DTS track just fine.