snoopy all your scans say your DW1620 is still using G7Z9?
Really, dont to that. If you did update, it did not work. I would recommend you to update to G7P9 which is the latest OEM firmware you can get from BenQ United States site (Europe still had G7M9 when I looked the last time). The only G7T9 I found is from shuttle.com and until now I did not hear too much good of it (thread somewhere below in this forum). I will post if I dare to try it, but so far my BenQ is fine with G7P9, so why change?
Also some ppl talk about first flashing to G7L9 (as L9 appears to clean sth out in the settings or whatever) and after the obligatory 2 reboots to G7P9. Look in this forum for infos about upgrade! Best done in Windoze safe mode...
And of course you also have to write the disc with the new firmware, be sure you do not rescan the disc you wrote with G7Z9. Throw it away!
Get some media other ppl here like, like Verbatim MCC03 DVD+R 8x Azo Layer. Dont waste too many, try one, it should give you good results. And dont write a disc of those before you are sure your DW1620 is updated to some good and recent firmware.
As some ppl here stated correctly, the jitter looks bad on the disc. If you are on P9 or T9 firmware, installo QScan and let it scan one of your discs. Maybe you just have bad/ake media? It happens all the time, I already had bad Sonys and bad TDKs. Let qscan scan the media at the recommended speed for that DVD and do a "full" test - if the curves display look like a roller coaster, chances are the drive will have problems writing excellent discs.
With DMA and stuff, your hw setup appears to be good. Look in services.msc whether IMAPI stuff and maybe Nero InCD stuff are running. I kicked InCD again as I dont trust it. And Win XPs IMAPI crap should be disabled, too (IMO).
EDIT: Ok, the first scans, I see, are B7T9. Maybe try to flash to B7L9 in safe mode, do the two reboots, flash to B7T9 in safe mode, do the two reboots and try again. Sorry for reading to fast (32x)
EDIT2: I suppose you have no harddisk on the secondary IDE? Only the BenQ? or is there some other DVD-ROM/CD-Writer/whatever attached there? If, try to disconnect it temporarily and test again. Make sure the BenQ is master and connected to the outer (black) connector on the 80w cable, not the gray one. The Blue one is connected to the mobo of course? Put in a pressed DVD-ROM or known good written DVD+/-R and do a burst rate test with CD DVD speed - for me it shows sth like 23MB/s. Should not be slower than that!