True story... The Game Gear TV adaptor has an A/V input. You have to have a cord that converts the composite audio/video connection down to a 1/8" mini plug.
So when the OG Xbox came out in 2001, I had a teaching gig. Went to the store, picked up the Xbox, Halo, and Project Gotham Racing, then went to the school.
That day was a prep day for me, so what I did was hook up the Xbox under a desk, ran the A/V cord to the Game Gear, and that's how I got to play Halo at work on day 1. ;)