was just looking into this myself
the Sumvision TB32 appears to support 2 x 1.5 tb drives. The official line is 2x1tb max, but they are all over ebay with 3tb of storage (eg http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=370160928344). It's also pretty inexpensive. Hope that helps