NT 4 and enabling DMA

I have three IDE devices:

-Plextor 2410TA (UDMA 2)
-Quantum Fireball ST (ATA-33) not for boot, just storage
-Internal ATAPI Zip250

After enabling DMA in both IDE channels and rebooting, with CD writer and HD on Primary, the DMAcheck reports, “DMA not in use”. But if either devices is alone on the chain, “DMA in use”.

Why is that?
Should I manually change the IDE configuration in BIOS (instead of leaving them on Auto)??
Or what would be the best configuration?

I don’t want to chain the CD writer or harddisk together with the zip drive, that seems to bring the transfer rate down to PIO mode.

So, if anyone can enlighten me, thanx in advance !!

NT 4 SP5
PIII 600 768 MB (Intel 440 BX)
Adaptec 2940U2 SCSI host
Plextor UltraPlexWide CD-R
Plextor 2410TA CD-RW
Quantum Fireball 3ST (ATA-33)
Internal ATAPI Zip250