My apologies. I missed your response to my response.
It looks like you're trying to do exactly what I have done. I'm not sure what WinMFS instructions you are using but the ones that I know are correct are in the Drive Expansion Sticky Thread, internal upgrades section, Item 19-A
, Under "TiVo Internal Upgrade Instructions: Preserves Settings Only
". In Step 13:
In WinMFS, select File -> Backup to create a truncated backup. Remember where you save it.
When you select where to save the backup it's on your PC, so you don't expect the SATA-connected TiVo drive to appear for selection.
Follow those instructions very carefully and turn off virus protection while using WinMFS.