Um I have an 8 bay using a Fujitsu/LSI SAS controller http://docs.ts.fujitsu.com/dl.aspx?id=a9d368cc-687c-4ee4-a309-05a927bd1c5c and a 4 Bay Silverstone TS431S SATA HDD Storage Tower for expansion.
I didn't have to modify the controller firmware, it just worked out of the box. As the card has an unused external port I would think that a second enclosure would work fine. I've used up 9 of my twelve using an SSD as a cache but I guess I'll cross that bridge if I come to it.
8 port controller from Ebuyer, 4 bay enclosure and SFF8088 to SFF8088 cable from Scan.
Yes, it cost more than another Microserver.