Nero 7 problem?

I have 2 CDRW Plextor 5224AT. I choose “Use Multiple Recorders” to burn 2 disks at the same time, but they burn slowly about 20 minutes. In “Buffer Length”, it always show 95% and 21%. In Options/UltraBuffer, I choose “Manual Configuration”, I set “80”, but the problem still exists. I think this is Asus’s mainboard problem because my old computer using ECS’s never burn slowly (always finishes 2 disks about 3 minutes). In fact, I don’t know this is mainboard’s or Nero 7’s problem. Please help me

Computer 1:
CPU: 3.0 Ghz Socket 775
Mainboard: Asus P915GL
Ram: 2x256Mb
VGA: 256Mb Asus Geforce 6600
CDRW: 2xPlextor 5224AT

Computer 2:
CPU: 2.4 Ghz Socket 478
Mainboard: ECS 865PE-A
Ram: 2x256Mb
VGA: 128Mb XFX Geforce 5200
CDRW: 2xAsus 5232A3