A friend of mine has built a few of these cards and he is having problems with them also. He has been reporting problems to the author and he has been working on the firmware for the re4091 and i believe he said the luns are working for scsi card readers and stuff now. Initially he couldn't even get a real scsi hd working on the cards but i think that has also improved. I gather they just tested it with the scsi2sd 6x?
Note the BFG has documented problems with scsi as far as i know there is no solution yet.