Have you tried installing the chipset/storage drivers from AMD's website? Maybe they have a newer version than the one on Gigabyte's website. You may also want to try uninstalling AMD's storage driver and using the standard Microsoft driver.
From what you've described the drive isn't responding to ImgBurn's command, and in these cases the storage driver is most likely the one causing the problem.
By the way, your "Gigabyte SATA2 controller" (the GSATA2_x ports) is in fact a JMicron controller, and you can get the latest drivers for it here: ftp://driver.jmicron.com.tw/jmb36x/XP_Vista_Win7/
You could also try using your burner connected to this controller.