I feel fortunate to have one of the most responsible kids on the planet -- at least when it comes to taking proper care of electronics. (If only he were that responsible with his homework.)
He knows his way around the business end of a modern AV receiver. Being young and wiry comes in handy when you're plugging and unplugging components in tight places. He knows as much about putting a system together as your average Best Buy employee. Okay, make that MORE. :o)
And yes, I'll admit that having his own Tivo may be a bit of wretched excess. But it only has one, not both, of the tuners hooked up. That's where I draw the line.
Still, you haven't lived until you've played Smash Brothers in full surround with the sub blasting.
Most 9 year olds do :-). I was taking equipment apart at that age too - and learned about capacitance the hard way. I'll tutor math if I can move in and you buy me system. I see no reason that the size of the display does anything expect make his system cooler. I vote he gets it (I'm a psychologist so you owe me for housecall). Cool kid, cool dad, why worry.