Ok, something to add:
If I plug the Pioneer in master slave configuration with my CD-ROM on IDE channel 1, it is recognized as Multi Word DMA Mode 2 in WinXP. I'm already aware of this because it is a limitation of my particular mainboard (MSI K7T Turbo LE). To gain full UDMA rate, I had to put it on IDE channel 0. But doing this, the Hard Drive lost 8-10 mb of throughtput on IDE channel 1.
Now, I want to have my Hard Drive on channel 0 to get full transfer on it. I need it because I use my computer as a Digital Audio Workstation and maximum transfer rate could make a difference. If HDD is on channel 0 I must put Pionner and CD-ROM on channel 1. As I said, I'm then limited to MWDMA 2 (theoritically 16 mb/s). In fact, device burst rate shows 13 mb/s in CDSpeed. I understand that it will limit writing on DVD medias to 8x maximum. It do not bother me because I mainly use the DVD Burner as a backup solution. I'm not doing any DVD ripping and it is ok for me to use only 4x medias (I'm not interested to pay more for 8x or 16x medias).
But I have a question : Will I be limited too when reading DVD or CD medias?
EDIT: I already answered my own question: CDSpeed ends at 40x when reading CD's in PIO4. Same thing in UDMA4.