Sorry for my bad english. Pherhaps I haven't made myself understood very well, but I don't think I'm contradicting myself!
I already know the CFModGuide, and I performed exactly the explained procedure when I modded the player.
The "ata error: -80" when trying to boot on CF is a known issue with at least many CF cards, also reported in the link you posted:
"Turn the iriver on with HOLD enabled to enter the bootloader configuration, and proceed to boot the RAM or ROM image. (If you boot the ROM image, you again get ATA -80, of course). You can also make booting the RAM image default. (For me (DavidAJohnston) both RAM and ROM booting work -- booting from disk is the only one that produces ata -80. Since this doesn't seem to be consistent, my best suggestion would be to use whichever one (RAM or ROM) works for you) "
I have the last bootloader (V7-pre4) neverthless the player only can boot the RAM or ROM image. Setting the boot to disk, i get the the following error:
ata error -80
insert USB cable and press a button
and successively
no partition found
In evidence the Trascend Premium 400x isn't fully compatible.
A part this issue the player works very well, booting to ROM image is very fast, and until this time I thought there wasn't any problem, as I never tried to upgrade rockbox before!