As soon as you pause live TV, then you're using the DVR. I don't know why anyone would have a DVR and not use it, or how anyone could use a DVR and ever go back to life without one, as you said.
ryu4000, why do you think you need a Homerun for live tv? Why do you not want to use a DVR? Are you going to use extenders, and if so, what do you have in mind? How are you going to get the signal from the PC to all your tv's (wired ethernet, Moca, powerline ethernet)? Is your HTPC going to serve purposes other than just live TV?