What could be the difference between a CF card in IDE mode and an IDE Harddisk?
Perhaps idefix doesn't like that the CF card will report itself being a removable device. This same behaviour is an issue with windows, but not with linux, so this can make a difference between different ide drivers in the Amiga system.
I also think I have seen a CF card actively pull down the IDE interrupt request signal line (towards 0V). [d] Then it should not be connected directly to the IDE cable, if there are other drives on the cable. The irq signal may also be connected together on all connectors of the 4-way adapter, so a CF-card can then be the only device on it. Because the drives should only actively pull up this signal, and pulled down by a resistor. You shouldn't push a signal up towards +5V and pull down at the same time. The IDE<->CF adapter might fix this issue.[/d] I checked this from an IDE standard draft, and I think it didn't say the drive can't pull down the line, if it is selected and nIEN bit on a control register is on.
Does the CF card show up with idefix drivers, if the CF card is the only IDE device connected to the 4-way adapter?