I hear that the esata ports on the back are not powered ones - you'll need to supply power through the enclosure or through USB.... check enclosure documentation.
Intel Storage drivers: http://downloadcenter.intel.com/Detail_Desc.aspx?agr=Y&DwnldID=15251&ProdId=3018&lang=eng
(choose the last one for 64-bit drivers)
Not sure if you need to do anything else, but you MAY need to poke around in the BIOS for
an esata enable/disable feature.. (you may need to configure them as RAID - I don't really know, as I haven't tried esata,
nor found anything that describes enabling them beyond what I have said.)
Try installing the drivers, get a self-powered enclosure and try the eSATA ports before messing with the BIOS.
The ports may already be enabled.
Facing problem with rear eSATA with WD My Book external HDD connected with eSATA and i got some clue from
in "http://tinyurl.com/yar9b5m" (incompatibility of the Marvell eSATA controller and the chipset on the external hard drive).
I hope its not with any specific HDD connected to DX58SO using rear eSATA Ports.