That's a pretty crappy datasheet; best I can tell from it, VREF is some kind of voltage reference to allow you to set the voltage on the output (so even if you have a higher voltage supplying it, you can output a lower voltage, I'd imagine). Not sure how it is set (current based?) - maybe thru a resistor (setting the current) tied high or low? As far as RIN is concerned, that is a real mystery; according to the block internal diagram, it leads to some kind of "amplifier" or "buffer" - but why? Not sure...? Hopefully someone else knows, or has a better data sheet. I am not really sure if these pins are strictly needed for all applications; can you tell on the DVD player where those leads go to (maybe to figure out how they work/why via a small bit of reverse-engineering)?