The Tower Pack DLC consists of a starting Horde with Human enemies.
After that you have this path :
Horde 1 Enemies Nosalis difficulty is Normal High or Huge
Horde 2 Enemies Nosalis difficulty is Normal High or Huge
Horde 2 Enemies Humans difficulty is Normal High or Huge
Horde Final Enemies Nosalis
Do to the fact that the waves are time based I suggest a "trick" that you can do in one of the Huge missions with Nosalis........you have to wait the end of the horde running running and running.
The Nosalis will hit you sometimes but you can manage this with no problems.
You can't do that in the stage with Humans cause obviously they have weapons and can hit you easily even if you run.
Hope this may help and sorry for my English.
Thanks to Dulfin that gave me the idea posting a comment in the "Test Complete" achievement.