Media center does work, but it's a pain to setup. Try searching on google for a guide.

The url you said about has changed

http://www.xbox.com/en-US/pcsetup/alldownloads.htm

Are you sure you haven't misinterprated killstreaks carrying over. It sound the same as COD4's if you die with UAV etc available it's still usable in your next life.

Making it so death didn't interupt a killstreak would break the meaning of killstreak rewards.

If if it worked like how you believe ground wars 9v9 would be a bunch of people reaching 15kills over the entire game around the same time all trying to bring in there kill streaks at the same time.