The Slingbox PRO HD does work with the digital cable signal. This information is included in our website. The following link will provide you with this information.
In this case, you can take advantage of the Slingbox PRO HD internal tuner. You need to set a splitter on the coaxial cable that comes from the wall.
Then, you need to send two lines from the splitter. The first one goes to your Slingbox (basic cable service channels) and the second one goes to your set top box (digital signal). This way, you will be able to select among the two options: the coaxial connection and Component / Composite connection.
You can also check this link in order to get further information.