Some (not very many) support PCM out of the digital output. A lot of them also can be software configured for specific cable companies. So, its kind of hard to tell whether your RCA digital output can be fed into a two-channel DAC or not. Most cannot.
That said, I've got a Scientifc Atlanta 8350HD, and there is a menu setting where I can tell the box what to send over the coax digital out. That works fine. You might just check the menu settings to see if there is some ability to modify what goes out of the box. AC3 through a 2CH DAC will not sound like music.
That said, I've got a Scientifc Atlanta 8350HD, and there is a menu setting where I can tell the box what to send over the coax digital out. That works fine. You might just check the menu settings to see if there is some ability to modify what goes out of the box. AC3 through a 2CH DAC will not sound like music.