I'm not familiar with the HDHomerun or the way it interacts with your PC, but I had a similar problem with my PCIe tuner card. What you can't do very easily is swap from one application to another because the card gets 'locked in' (for want of a better phrase) to that application.
For example I had my card working perfectly well in MC16, but I installed MediaPortal to try and mess around with DVB-T2 and DVB-S&S2, and then channel scan on MC would do exactly the same - find no channels. I had to completely uninstall Mediaportal (not just disable the service) to get the channels to rescan in MC. I haven't tried 7MC, but it may also 'hog' the connection to the tuner.
SBR