The LiteOn 400D is a rebadged DRU-500A (not the other way around). As such it isn't a LiteOn drive but a Sony one.
The 400D was the first DVD burner released with the LiteOn name on it and to me it seemed to be a filler until LiteOn could get it's own model out. AFAIK there are no hacked versions of firmware for the 400D. You would probably want to stick with the Sony firmware as LiteOn didn't support the 400D for very long.
Actually, just looking around it appears that Sony offered a free firmware upgrade to the DRU-500A that bumps writing speed up from 2.4x to 4x if you didn't know already.
Check it out here.
Moved topic to Recording Hardware forum as it's a Sony and not a LiteOn drive.