Both BTV and Sage will work. If you want a full multimedia (music, photo, video and TV) use Sage. If you only want a TV PVR then BTV. BTV is the best (IMO) PVR software for North American TV. Both have great user forums and work well
Be aware that you will need a pretty decent PC to handle the HD PVR playback and there is a fair amount of setup required to get the QAM channels mapped on the HDHR.
Your question makes you sound pretty newb to the HTPC scene. Your proposed setup is pretty sophisticated with 2 x cableco STBs, 2xHD PVRs and a dual tuner ATSC/Qam HDHR. If you are a newb, you will have dificulty in getting them all playing nice together.
If you are not a newb please forgive the assumption.