It dosn´t sound good if you have to disable Domain Validation (on your adaptec 29160?), this feature testwrites to a device and lowers the speed if the data contains parity or crc errors. So if your speed is dropping when Domain Validation is on, you have something that corrupts the data when transfered at high speed.
Do your mobo have via southbridge? If so - then it could be this which makes the trouble, there are theories that via mobos generate electrostatic-noise under xp!? A lot of people with VIA-chipsets have problems with setting DMA on IDE in XP, because XP has the same sort of feature (Domain Val.) for IDE. I have this prob. with my PC with the Asus A7M266 mobo (and the geforce/nvidia infinte loop crash lol ).
The PC with my recordingspeed prob. is a pure AMD 762/766 chipset, and disabling the Domain Val. doesn´t help.
Let me describe my prob. in more detail: In Nero when selecting "determine maximum speed" Nero tests my hd-speed before burning and indicates before the burningprocess that the max. transfer rate is 23X (3450 kb/s). Sandra tests it as approx. 75.000 kb/s (4x scsi160 raid). That is for starters a great reduction.
But furthermore - when the burnprocess begins (the speed will still be measured under burning, when "determine maximum speed" is selected) it only reads from my hd at half the previously determined transfer rate eg. 11,5 x speed. (And it is exactly half the speed, and just 0,5 x below the max speed of the recorder. Plextor 12/10/32S).
So what i am asking is that people with underrunprobs. i XP, should try to "determine maximum speed" when burning in Nero and see if it yields the same result or simular.
I have tried all the driver/patch-combos from Nero/Adaptec/MS, and they do not help or even change performance. So installing the new ASPI-layer (4.7) doesn´t hurt, but I can´t tell if it´ll do you any good!?