I think you have a problem... SME already supports UDMA modes.
I´ve seen 20MBs on hdparm.
You can check the drives status with:
hdparm /dev/hda
or whichever drive you are interested in. You are interested in the 'using_dma =' line.
If it's set to 1 (on), you're OK, otherwise there was a setting in 5.6 (don't know if it still valid) of:
/sbin/e-smith/config setprop hdparm status enabled
which will enable dma at the next boot.
You can check if this option has already been set with:
/sbin/e-smith/config show hdparm
Trevor B