Next time you have a black screen, see if you can restore picture without rebooting by trying the following:
1. Unplug power to the tuners and replug (wait for the bong/bong when you unplug and then wait for the lights to come back to green/green) and check
2. If that doesn't work, try switch user and sign back in.
3. See if the problem exists on any extender as well as the media center
Each of the above would point in a different direction so see which will restore. If the first works, then you have some task that's running (some scan) that's looking at the USB ports and disrupting the tuners. I don't know of any DRM that time warner can sent short of unauthorizing the card. They can updaate the VCT but if you have M cards that sholdn't matter. With S-cards that could require a reboot but it wouldn't happen that often.
The other tests would point to software interferrence or a driver conflict with your video card.