One of our existing R10's is starting to give up the ghost. I noticed DirecTV is offering one of the HD DVR's for $99 right now. Will getting one of the HD units work with my existing SD only setup? Eventually we want to move to HD but it's not a pressing issue at the moment, and I was trying to decide between getting the existing unit upgraded at someplace like Weaknees but, I thought it might be time to migrate over to the DirecTV HD units. Assuming the HD unit would work in our SD environment (i.e. we wouldn't be swapping out the dish, switches etc.) besides the obvious, that we couldn't watch HD channels would we lose access to any of the other features like the DoublePlay, network connectivity, etc.? Thanks!