Here's mine. It was manufactured long before your one but that shouldn't make a difference. Whilst I guess it's possible they've now dropped the overburning feature, I don't think they'd be able to do so whilst keeping the 'PLUS' name. AFAIK, overburning was the only thing the 'CB-PLUS' added over the basic 'CB'.
I've asked a contact a Vinpower to take a look at this thread. Hopefully he'll be able to work out and tell me what went wrong and where!
EDIT: Hi Liggy - yeah, I have 1.Z8 on mine and overburning is still working just fine.
Optiarc DVD RW AD-5280S 1.Z8 (ATAPI)
Current Profile: DVD+R DL
State of Last Session: Empty
Free Sectors: 4,267,040
Free Space: 8,738,897,920 bytes
Free Time: 948:15:65 (MM:SS:FF)
Next Writable Address: 0
Supported Write Speeds: 4x, 6x, 8x
DVDÂ±R DL Boundary Information:
L0 Data Zone Capacity: 2,133,520