Yeah, I tried that, too, although the SAT button didn't blink twice. All the device buttons kept blinking until I released the SAT button. Then I followed the instructions for the 990 blink back and pushing buttons 1-4 gave nothing. When I pushed 5, it just transmitted to the SAT box. According to strict interpretation, this means I have a 4-digit device and its code is 0.
Which manual did you look at? The only one I found just tells me how to blink back the code for my TV.
There might be something in that. I seem to remember the tech support woman telling me that the only thing I needed to look out for is getting an after market remote that is UHF-compatible.