It doesn't matter which adapter I designate slave or which card I stick into which adapter. 9 times out of 10, the thing won't boot correctly and HDB is always what gets hung-up.
Not all CF cards will ever work correctly as "slaves". I think the original CF spec assumed master/single drive configs, but my memory is fuzzy about that now.
The CF cards may not be 100% compatible being accessed as IDE devices (probably a long shot).
Not an issue. "IDE" mode is the normal access method for CF cards.
The IDE-to-CF adapters may not be compatible with cards over a certain size.
You can rule that one out, too. The same pins are required for any size drive, from 1MB to 2TB in size. So it's not a drive size issue.
One of the adapters may have grounded out on the drive carrier.
That's a good and likely possibility, and not too difficult to troubleshoot.
I do have a couple of empegs here with dual 16GB cards installed and working.
Cheers