I did a bit more reading on the net and it is possible to split sata connection but it would required a port multiplier which cost about $100 and the express card has to support port multiplier as well
I think i will ended up buying a single sata case with hot swap function.... and build a HTPC / server in the end.
I did consider raid 0 but 3TB is a lot of data and it cost quite a lot to back up those data. Unless the price of 1TB drive drops, I will just back up some of the important data.
I would recommend one of this:
http://www.geeks.com/details.asp?invtid=EN391-S2HC&cat=RDM
I just swap in a new HD when the old one is full.