I'm using a sat-pata converter because my motherboard is VA chipset and can't remap to primary and secondary channels.
The other 2 jumpers are one connected directly to the main Marvell chip, the other to the motor driver by a resistor and a capacitor, i'll try it later.
btw:
ENG>HELP
DC MC BT PK DM MM SD SM VU CC EP EC SV XN XW XR
XS XC XF XH XT XD XL XP XA HE RT D DP DB DW DF
DI M MD MB MW MP MI FB FW SB CA RC BI DN DU LW
LP LD FI BD BS BC GO R2 T2 SS NS DA DR MR
ENG>
ENG>BD
BREAKPOINTS AT:
ENG>FW
E:0003 - Req Prm
ENG>GO
E:0004 - Dbg Cmd
i'll have a dead hd next to a dead 360 soon

I know that this thread is VERY old, but did you get any more info on the serial commands? I'm looking to change the serial number on a 20GB Samsung HD.