Dma mode for nec burner

I am contimplating a new dvd rw and have two in mind 3500 and the 108. But my question is I was reading in another portion of the site about dma 2 vs 4. They say that 4 is faster than 2, makes sense, but I can only get mine to dma2 and I have 80 cables, round 133. my hdd run dms 5, and on the promise card they run dma 6. is there anyway to up the dma that I have maybe missed. I have been in the bios and manually config to dma 2 the highest avail. My current drive is a 2500. thanks for the help.
does anyone know if I can run a cdrom on the promise card on a p4c800 dlx if set to ide