Improving TDM AI´s

[Suicide Junkie]

If you're looking for more challenge from the AIs because you can stomp high bonus TDM, and want to play with modded files, you could try Carrier Battles.

I play CB with no bonus, team mode, ~6-8 AIs and it is tough. No cheating! Anything they can do (except treaties of course), you can do too... but you need to pull out all the stops and play your hardest just to survive.
A low bonus game might theoretically be possible to survive if you can play politics to keep the AIs fighting each other... Rollo tried low bonus, and had thousands of AI troops on his homeworld by turn 30 or so.