I got the same problem. ANY media burning only at 6x.
My board has a VIA KT333 chipset. I tried all available Bus Master drivers and yes, always using DMA Tried all available IDE ports. Tried 80 and 40 pin cable. Tried different firmwares (101,102,103,104). Always the same result. I attach a typical "data disc" burn session. Using MCC003 with FW103, but it looks the same for any medium I tried so far (all DVD+R available here).
I also tried the device in another System (with KT800 chipset). Perfect burn there with the same FW and MCC003 medium (same spindel)! So the drive is not damaged. But communication between board and drive is not ok. Nero burns with flickering "buffer level" but without problems in the (hdd) read buffer.
At the KT800 system Z-CLV was used. Is there a trick for activating P-CAV? I mean: the burn process was not "round" but had three discrete levels (steps): 6x,8x,12x
On the attached jpg you can see the drive tried to move from 6x to a higher level but failed so it continued with the "safe" 6x speed. Is this normal? I only see round curves everywhere in the forum.
Any idea what could fix this issue?