The Slingbox Pro has a coax input and an analog tuner. The coax output does not need to go to your TV. That feature is optional so that you can watch it locally. You can plug in your cable feed directly into it, configure the ANT IN video source, and see if you can find any available channels. Unfortunately, the analog tuner is a bit dated due to the digital TV transition. So, you may need to contact your local cable company for a set-top box with the ability to tune, decode, and decrypt their digital signals.
Alternatively, the Slingbox Pro-HD has coax input and a digital tuner. It supports unencrypted Quadrature amplitude modulation (clear QAM), Advanced Television Systems Committee (ATSC), and Over the Air (OTA) signals.