I have the SA 8300HDC from Time Warner Cable, and just starting messing around with the firewire port today. It seems as if it only outputs pre-recorded content. Live TV, wether it be basic or premium channel, my MacBook wasn't recognizing a stream.
BTW I'm using AVCVideoCap, which is part of the Apple FireWire SDK, for capturing.
Now if I could only figure out how to encode the resulting .m2t files to something suitable for making SD DVDs. I've tried .avi, .mov, .dv, divx and XviD, and the audio has either been missing or gradually goes out of sync.