Ratpack,
If you use an external HD cable box, it will function as the system's SD and HD Tuner, bypassing the Samsung's internal HD tuner. In fact, there are significant differences in the quality of outboard cable boxes' tuners and scalers/deinterlacers.
Cable-card ready HD sets have internal HD tuners, which may be superior or inferior to an outboard cable box's.
In my own case, my Samsung is an HD-ready set that lacks the internal HD tuner, so I must use an external HD cable box to receive HD channels.
The previous outboard cable box I used, a Pioneer Voyager supplied by Time-Warner had really mediocre quality on SD and non-HD channels. The replacement, a Scientific Atlanta 8300HD DVR with two internal HD tuners, is much superior to the Pioneer HD box. My non-HD and SD channels are mostly quite good. HD performance of the two different outboard cable boxes is similar, although the Scientific Atlanta is more versatile in a number of respects.
So it's likely that in the case of the cable-card ready Samsung, its internal HD tuner/scaler is superior to the outboard box that Time-Warner had previously supplied.
Regards,
