I actually had an optical cable lying around the house, and hooked it up. The sound was really good, and as I was going through the "setup" on the RNG110, I noticed that "highest" output was "stereo". I have seen Comcast advertise that some programming is 5.1ch, but the cable box seems to only output stereo. Regardless, the sound was good. After enjoying it for a little while, I ended up disconnecting it because it is not a user-friendly setup.
While the cable box is on, the BD player is in some sort of "sleep" mode where it passes on the sound without being on completely (which is good). When I want to watch a Blu-ray, it stays in this "sleep" mode even after I turn it on. And when I want to change a setting on the Blu-ray player while the cable box is on, I can't because it's in sleep mode.
It's nothing overly-difficult, I'm just not satisfied with the awkward steps I have to go through in order to make the Blu-ray (and A/V) receiver function the way it should in all situations without going through tedious menus every time I want to watch a movie (like change the "output" sound on the cable box from "TV speakers" to "stereo", and then back again when I'm finished). I would rather have a more seamless experience and separate the cable box from my Blu-ray player, rather than mixing everything together and having to mess with things every time I want to switch back and forth.
Also, every time I would change a channel when connected to the speakers, the sound would either be very low, or way too high. When I put the volume higher on the lower-volume channels, and then switched it to another channel, the volume would blow my ear drums out!
If I ever wanted to be serious about this, I may hire a home theater guy to set things up correctly...