I looked through the manual for the Panasonic DMR-EZ48 (first one I came to). There is no indication that optical output is ever disabled, although as with any DVD player it can be set to either PCM output or bitstream output (done to accommodate those rare devices that have digital inputs but no Dolby Digital or DTS decoders). The HDMI port can be configured to either output audio or not output audio, but there's no mention of what form that audio is in - I suspect that it mimics the optical output, but I could be wrong. The specific manual can be found here , but it's a big file (something like 27MB). If you look at it, take note of pages 61-62 (digital audio output settings for Dolby Digital and DTS), 66 (HDMI audio output), and 72 (optical and HDMI connections).