I want to buy a DVR and I want one with this function: I want to record a show (say, Simpsons), watch some of it, record another (say, ALF), watch some of it, and go back to watch Simpsons EXACTLY where I left off. I basically need to be able to set multiple "positon memory" points (or have the device automatically do this for me). I want the machine to know where I am on each show it records for me. Which device can do this?