We received the add on card in a package with the card U3S6 and an enclosure with a Seagate SATA2 HDD inside. The enclosure uses a ASM1051-SuperSpeed USB to SATA Bridge Controller. ASM1051 is a single chip solution designed to bridge USB3.0 to SATA Gen 2, and has already passed the Electrical Specifications and Transmission Protocol validation test of PIL (Platform Interoperability Lab). See how it performs in our review.
http://www.ocworkbench.com/2009/asus/ASUS-U3S6-USB3-SATA3-card-review/g1.htm