You made sure the Tivo is set to Dolby Digital (NOT Dolby Digital to PCM)?
Maybe you inadvertently changed a setting on your receiver?
Try switching to Dolby Digital to PCM and then back to Dolby Digital.
If that doesn't work, try rebooting the Tivo.
Originally Posted by Larry M
If the TiVo passes Dolby 5.1+and does not do the decoding itself like the Roku does, then optical will not carry that signal. Only HDMI can do that.
Optical carries Dolby 5.1 just fine.