I finally got a hold of both Duke 3D and Quake. I saved both games, which goes to the internal memory by default. I then copied both save files to the backup cart. When I went to play Duke again, sure enough I found the option to play Death Tank. I tried it out, but right in the main screen for it where it gives you the directions, it says it is for 2-7 players. In other words, only one multitaps worth.
Since I only have two multitaps right now, and only 5 controllers so far, I had no way to test to see if it would allow me to play with more than 7 people. However, I doubt it would lie in the directions, so for now I'm going to assaume it only supports 7 players. It seems many of you are from Europe, so perhaps your PAL version of the game was different than my NTSC one, and supports 16 rather than 7 players?
Either way, I need to get 5 more controllers regardless, so I can support the full 10-player madness that is Bomberman! Me and my friends have already tried it with 5 people, and it was a blast (no pun intended...). Once I have all 10 I can try Death Tank again and see if it really supports more than 7 players. And since no one else has been able to inform me of any games that support 11+ players (despite the fact that with 2 multitaps you could clearly have up to 12 players), I think I will just stick with 10 controllers for now...
For those wondering, Death Tank is bassically just a rip off of the classic old PC game "Scorched Earth", although I really don't know which one came first. Bassically you have a little stationary tank, and you can adjust your firing angle and power, and try to blow up everyone elses tanks. At the end of rounds you get money and can buy better weapons and other powerups. All in all pretty neet, espescially they way they hid it in another game.