I just bought a Plextor 708A and I cannot get it to run in 8x burning mode. I did some research and deleted the secondary IDE channel and rebooted.
All the channels are in DMA 2 mode and my Lite-On 52x burns CDs at that speed with no problem.
Asus P4T mobo
Plextor 1.0.6 firmware
Ritek G04 DVDs
Here are 2 screen shots.