I'm not sure if I can help or not, but have had a problem with digital audio with Time Warner as well. I have a high definition cable box offered through TW. On certain high definition channels I would get audio also going in and out. Sometimes it would correct itself, but on one particular channel it would not. When I had TW come out, they didn't seem to know what the problem was, but said I had one of the older boxes, so theu replaced it with a newer high def cable box. Problem solved! You said this is your third box, so I am assuming you have had TW out to try and fix the problem. I am thinking maybe see if they have a different make or model box you can try. Just a suggestion. Hope this may help.
