Yeah, but I'm not sure what you want to break down?
(I'm sorry it seems to be a bit off, this could be a simple addition error on my part)
We get 6 castings of greater arcane fusion, and each casting gives us: 12 Maximized and empowered magic Missiles + 8 Empowered Magic Missiles, so we multiply 6 by the number for each casting and get ourselves 72, Maxmized and empowered missile spells and 48 empowered magic missile spells.
We also had 6 castings of greater arcane fusion in the last round, they were repeating as well, and all the missiles in them were repeating, and so were the lesser arcane fusions in there.
For each greater arcane fusion there is also the missile that repeats and the lesser arcane fusions that repeats, let's calculate how much that is per greater arcane fusion:
Each Arcane fusion gets 12MA+8EA, All these missiles also repeats, so thats 24MA+16EA per casting we had in the last turn. Then there are the repeating lesser arcane fusion, an arcane fusion that is not twinned gives 2MA+2EA (due to them being twinned), but there are two castings of arcane fusion and they are both twinned, so we double it twice, this gives us 8MA+8EA.
So we add these numbers together, 24MA+16EA+8MA+8EA = 32MA + 24EA. This is for one Greater Arcane fusion cast the turn before, however, we cast 6 greater arcane fusions in the turn before, so we get 6*32MA +6*24EA = 192MA + 144EA, just from the repeating from the turn before.
Now we add these 192MA+144EA to our 72MA+48EA Which gives us 264MA+192EA.
We multiply by damage per spell to get:
264*150+192*127.5=64080
The trick here is that when you have repeating spells inside repeating greater arcane fusion the repeating ability triggers alot of times. Also Twinned spells inside Twinned spells gives a HUGE doubling.
Hope this clarifies it a bit.
EDIT:
Filling out this it would look like:
With Magic Items:
Most Damage -- Single Missile: 25
Most Damage -- Single Casting (with the repeating ones next turn): 44*150 +32*127.5 = 10680
1-Round Total Damage: 64080
Highest # of Missiles -- Single Casting: 6*76 = 456
Highest # of Missiles -- 1-round total: 6*456 = 2736