[rockadanny]

In my quest for an inexpensive solution to crappy TV sound I am at the point where I am considering T-amp and bookshelf speakers (dislike soundbars and Zvox box is too large). Since TV has only one audio output - optical - I was considering tapping off the cable box (Comcast) RCA outputs. But now I read that some people have had audio (lip) sync issues doing this, though not specifically with Comcast. (Audio and video out of sync.)

What would cause such a thing?

Also, do you know if I might have this issue were I to connect to the optical audio out of the TV instead? I was avoiding this solution as I'd have to buy a converter (optical-to-analog) to do it this way. 

[Phil A]

I sometimes have an issue with the kitchen TV where I got a digital video (over-the-air) signal and it is broadcast in Dolby Digital and I have it converting to just the TV speakers as that's all that is hooked up to it.  So I'd guess you have a similar thing going on where you have audio and video delivered by different means.  I'm not sure a converter box will resolve the issues.