Currently the InfiniTV4’s native support is limited to 7MC; however, Babgvant (Andy) released SageMCTuner that lets you use a CableCARD in SageTV. It is limited to Copy-Freely content and has a delay.
With CableLabs’ approved change to the OpenCable specifications Ceton + SageTV will be able to add native support for the InfiniTV4 + Copy-Freely content but currently no ETA for that.