Amongst many, I used a Zu Firemine that I liked best. It was very reasonably priced but I'm not using it now because I jumped from the DacMagic all the way to the McIntosh MCD500.
http://www.mbd-indo.com/Product/ZU/Firemine/Firemine.html
email me for more info
http://www.mbd-indo.com/Product/ZU/Firemine/Firemine.html
email me for more info