I'm not 100% sure to be honest. There was some mention on the old A4000/5000 yahoo group about it, I think you needed an ide/scsi convertor so you could use an IDE reader with the Scsi interface. This gave me the impression at the time that ide card readers wouldn't work on the A4k's ide interface. I could be wrong.
I been waiting/searching/trying for years to sort out a card reader for my A4k, the hdd I got in there right now is noisey as h**l.
I love my A4k, so very tweakable, it's great.