what is the significance of this spec? for ex., NAD 773/763 are spec'd at 50 mHz video bandwidth. Denon 3805, Arcam avr-300 and some others are 100mHz. what does it mean, and what do you need for HDTV? i thought i once saw a web page w/a formula showing bandwidth as function of lines of resolution, frequency, and a third variable, but i can't find it.