AvG,
I didn't say it was a waste of time, just a waste of money for a big dollar digital cable. I have my cable converter/DVR connected to the DAC in my Resolution Audio Opus 21. It sounds much better than using the analog outputs from the cable box. However, I didn't notice any difference between a bargain basement digital cable and my Stereovox.
It is certainly worth the effort to connect the cable box into your system using a quality DAC. I just don't think you will get much additional value from a big-bucks digital cable.
Enjoy,
TIC