Here is my take on the All AP dream team. If you take a moment to think about this and why it works, you will see how simple and easy this idea is.

This team comp relies on items and abilities to lower the enemy's magic resist to 0 and negative. This means that all of the abilities of every champ involved will do true or even bonus damage. This is good for scaring the pants off of the enemy team, forcing them to abandon their usual builds and stack magic resist. This not only shuts down the damage output of squishies but even makes tanks that stack MR seem to melt.

This team comp relies on items and abilities to lower magic resist, making all of those abilities stronger.

Items: Abyssal Specter
Will of the Ancients
These Items work really well for this group. Abyssal Specter is the item of choice, and WotA is the lifesteal that changes this fight.
Note on Items: Unique Auras stack as long as they are on separate champions. E.g. Amumu and Soraka can both have Aegis and both will have an effect, but two on Amumu and only one aura is in place.

Abilities:
Amumu's Passive: Cursed Touch
Karthus's Wall: Wall of Pain
Fiddlestick's Passive: Dread
Ryze's Bouncing ball: Spell Flux
Soraka's: Starcall

ALL of these abilities lower enemy magic resistance. Total MR reduction at all ranked up abilities, assuming all are in effect: 103 with only one starcall in effect. This does not even take into account the auras from the Abyssal Specter's which would lower the MR by another 40 points. Esentially, any resistance is futile. Even if only half of these effect are in affect at any one time, nobody but an MR stacking Galio will be able to do anything.

Early game: Karthus mid, Fiddle solo's top, Amumu starts at blue pulled by Karthus, Ryze and Soraka duo bot. Early game will not see too much action. Focus should be on farming for items. The builds above do not show it, but you should be rushing aura and teamfight items such as Aegis, Abyssal Scepter, and Will of the Ancients. By the time the teamfight/ ganking phase starts, this plan should be in full motion.

Mid game: teamfight time. Time to shine. Amumu is the tank and initiates as always. Focus on autoattacking the other champs (each one once) to maximize the magic reduction. As a goal try to get them all close together. Fiddle can jump in with his ult, Karthus lays down his wall, Ryze bounces his ball, Soraka heals as needed and starcall's on cooldown. Any squishies by now have negative magic resist. A Karthus Ult usually wipes them, and you are free to push.

Late game: Continue the builds and build up the beefiness. The game has gone this long for one of two reasons, the enemy team has been picking off stragglers, or just turtling. More defensive items are the solution. This way you can either tank turrets, or last until your teammates show up.

The biggest enemy of this team is the dreaded Silence. To be targeted first and bursted down are champs such as fiddle, Cho, Soraka, or anyone with hard stuns. This team has plenty of cc of its own, silence from fiddle, stuns from Amumu, silence from Soraka, slows from Karthus, and so on. A little bit of practice and this idea will most definitely fly.

That's my take on when everyone wants to be AP. Leave a note in the comments if you have any suggestions.

Harbringer91