Hi there! I’m from Portugal and my english is not very good, however I’ll try to share my experience!
All begun with a simple mistake, at a store I bought 2 ultra-speed cd-rw. when I got home I noticed that my GCE-8480B couldn’t write on them.
The search begun! 
I Updated it to firmware 1.05 but, sadly it wasn’t enough.
So I somehow understanded we coul have a “new drive” and not spend money!!
I got to read here that we could transform a 8481 in a 8520B so I thought: “8481?! Why not 8480??”
All in portuguese of couse!:a
So I’ve manage to convert the firmware of a 8480B to a 8520B and it is working, ultra speed compatible, but it only works with one light. 
who cares! I’ve just recorded a ultra speed cd-rw at 24x.
Came here to say, if you want to do the same there´s no problem, considering you do everything very very right! 
Thanks for all the help! 