I'm not sure about your description. You have the expansion box and "passive" adapter card, but not the cable?
cable driver ICs / line drivers would probably be necessary for anything longer than a very few inches. You'd probably get more length than the PCI cables available on eBay, but not all that much. It sounds like they may be implemented on the expansion box LoBo.
What connectors are involved on each end and what's the spacing of the contacts?
Alternate ground lines and shielding between multiple cables sounds like the bare minimum in terms of an extension.
Fabbing adapters for using the standard alternate ground line IDE ribbon cables might work nicely.
cable driver ICs / line drivers would probably be necessary for anything longer than a very few inches. You'd probably get more length than the PCI cables available on eBay, but not all that much. It sounds like they may be implemented on the expansion box LoBo.
What connectors are involved on each end and what's the spacing of the contacts?
Alternate ground lines and shielding between multiple cables sounds like the bare minimum in terms of an extension.
Fabbing adapters for using the standard alternate ground line IDE ribbon cables might work nicely.