I've never used 68 pin enclosures unfortunately.  However I would assume that it would be like the 50pin High Density connector (http://www.scsi4me.com/images/external-connectors.gif) where you would either need a 25 pin to 68pin cable with passthrough, or a 25pin to 68pin with an adapter, and a terminator (http://www.scsi-cabl...ator_cn50.jpg).

It may be possible to combine an adapter and passthrough terminator, but I have not tested that possibility.  Perhaps someone who has tested it can comment.