I've had some problems with my TiVo signaling the Sky Digibox. I'm using a Pyramid affair to control TiVo from the bedroom upstairs and these seem to be notorious for sending out spurious IR. This noise then interferes with legitimate signal between TiVo and the Sky box. So, I decided to try one of the new RF2Links from PaceLink.
The RF2Link is a "hard wired" solution that takes the IR output on the back of TiVo and inserts it into the Sky Digibox on its RF2 connector in the same way the Sky TV Link IR extenders do...