Which firmware for 3550A?

I just purchased a NEC 3550A DVD burner. I would like to get rid of rip lock and be able to set the book type to DVD-Rom.

I see that there is 3 different firmware versions.
1.04
1.05
1.06

Which one should I use and what is the difference between them?

Try the Liggy/Dee 1.Y6 firmware which can be found here: http://liggydee.cdfreaks.com/page/3550/

Thanks for the info. I see there are two versions of this firmware. One with RPC1 and one without. What is RPC1?

Have a look at the NEC F.A.Q. on this forum.