It turns out that The Face of Madness (Extreme) is actually possible, though very difficult and annoying. An easy way to make it a lot less annoying and slightly less difficult would be to switch waves 3 and 4. This gives more time for Wrenna to slap the Abomination+ around before the Death Worm+ get in the way.
Here's my setup:
Azra: Book of Blood, Furious Start. Max the red spells and put remainder of points in Healing.
Slak: Evni+. Max Slash, Double Hit, Flurry, Madness, Swiftness, Rage. Remainder of points in Resilience.
Ketta: No Deep Shot or Poison Shot. Only 1 point in Triple Shot (and keep it turned off), 5 points in Piercing Shot, everything else is maxed. In retrospect, Ignoring Spread Shot and maxing Poison Shot (only 3 points in Piercing Shot) might have worked better.
Wrenna: Beast Weapon+. Only 1 point in Sleet (and keep it turned off), 5 in Ice Spear and max everything else.
Markos: Eye of the Flame+. Skip Cleave. 1 point in Hard Knock, Stun Stab, and Armor Pierce. Max everything else except Armor Training, which is level 3.
Niru: 1 point in Epic Halitosis and Fatten Up, 4 points in Roar. Max everything else. Remember to disable his other attacks when you want to Nom. I did a LOT of micro-ing...although in retrospect, maybe the "CHEAPEST Technique" target option would have taken care of that.
Anyway, attached is a picture of the basic setup. Wrenna moves the the (1) spot when the Abomination+/Monstrosity+ get out of range. Slak moves to the (2) when convenient or if you are really worried. Markos moves to (3) in the direst of circumstances. Moving Wrenna happens every set of 6 waves except the first. Try not to do other moves... you'll need the psi.
Here's how it works:
Place Slak, Ketta, and Bakal immediately, DO NOT CAST FRENZY. FRENZY IS FOR KILLING ABOMINATIONS. When Snake Knight+ comes around, place Markos -make sure he has "strongest" priority. Then place Wrenna when things start coming out of her lane. Use knockback and then dragon fire to get past Snake Knight+ and Worm+ with a minimal amount of psi, but save your Crystal for the Worm+ that spawn from the Monstrosity+ that spawn from the Abomination+. Frenzy when the Abomination+ spawns. Use some lightning on the Death Worm+ as needed. Your goal is to get through the first six waves using a minimum of psi on lightning so as to boost Niru as much as possible as soon as possible.
Once Niru is fully boosted, move Slak around to follow Zelemir, and cast lightning on him as much as possible. I think I did around 3 million damage with lightning. Make sure you have enough Psi to move Wrenna around, or the Worm+ spam will be too much. Keep frenzy for killing the Abomination+/Monstrosity+/Worm+. Crystal, too. Dragon Fire is useful too, a little... though honestly I think I only cast it twice because I was holding it in reserve for emergencies. I won around wave 45. The really hard part is using enough Lightning on enemies so you don't get overrun, but not so much that you don't have enough Psi to do all the many things you need to do.
Sorry for the extreme detail, but I figure since apparently nobody has done it before, the detail was appropriate.
Next I'll try to figure out mods/tweaks that would make "The Way Out" and "The God-King Walks Again" possible on Extreme. I think TGKWAE will be easier to tweak than TWOE... but we shall see!