HDMI is an interface to allow for the transmission of video, audio, and control signals in a digital format. There is nothing inherent about it that will produce a better video or audio signal than other analog alternatives.

Your HD cable box however is capable of receiving HD digital signals and sending them to your HDTV without a digital-to-analog, analog-to-digital conversion taking place that will cause degradation. I'm not aware of any STBs (set top boxes) offering HDMI from an analog signal.

Most HDTVs nowadays can do a pretty good job of upscaling a standard definition video source to HD resolution. While not getting true HD signals from your other boxes, you may wish to try the component video outputs from the boxes to the HDTV, if the boxes have them available.

Even 1080i from a STB is not going to look any better in HDMI than component. A conversion from the "coax" (i.e. composite) to HDMI will actually only degrade the overall quality.

While "digital" has become a buzz word, really what it mainly offers is simply reduced bandwidth and storage space over analog signals, while attempting to not reduce the "perceived" video quality.

For cable you would need the HD cable box sorry.

stunning picture sounds like you have a HD tuner on that tv. what type of tuners if any do you have on the other tv's? our cable co basically scrambles all the channels now. either get a full on tuner or have a digital convertor for each tv. but the DTA is not HD. gotta spring for multiple HD tuners.