Well, perhaps it isn't obvious, but based on unofficial information (see item 1 in post #9), the IR signals needed to send e.g. rewind to a Sony HT system can't be generated using a Comcast remote. I've tried to explain why in posts #7 and #9. #7 mentions a few other remotes which will work.

If you want to experiment, you could try the Sony codes for DVD players. To do that, you can use AUX setup code 20533 (assuming you have a red OK/Select button). Any button for which you've already done a 994 keymove will still send the IR signal specified by the keymove. Other buttons will send Sony DVD signals.