I've currently got a round dual-lnb dish on my roof with two coax wires (and of course the ground wire) running externally down my home to a 3x4 multiswitch, with two coax wires going into one room for an SD-DirecTivo and one coax going to the other room for an old SD receiver. I'd like to replace the SD DirecTivo with the new HD DirecTivo (probably moving the old sd unit to the one-wire room and leaving it as a single-channel unit), and I understand I need to put up an oval dish with a built-in triple lnb. Can anyone tell me what this means for all of the downstream wiring and multiswitch? Do I need to run an additional wire down the exterior, or will two coax to the dish with some kind of downstream splitter/multiswitch do the job? My goal is to do this myself with the least possible additional wiring. Suggestions?