eSATA enclosure- can it support SATA 3?

I have a SansDigital TR4M 4 bay eSATA enclosure. It came bundled with a dual port card that supports port multiplier and can connect up to 10 drives in 2 enclosures. I'm wondering, if I upgrade the card to SATA 3 w/port multiplier would I get get 6 G/s speed with my installed SATA 3 drives? Is there anything that could be specific to the enclosure that would limit eSATA speed or is the enclosure just a way to power and connect the drives, the SATA speed determined only by the card and drives? The present card is described as 6G/s but that's because of its 2 3G/s ports. From System Profiler the card appears as below:

Card------------------------- Type-------------------Driver installed-----------------Slot
pcib4b,91a4------------------IDE Controller-----------------No---------------------Slot-3
pci1103,622-----------------RAID Controller----------------Yes---------------------Slot-3


pci1b4b,91a4:

Type: IDE Controller
Driver Installed: No
MSI: No
Bus: PCI
Slot: Slot-3
Vendor ID: 0x1b4b
Device ID: 0x91a4
Subsystem Vendor ID: 0x1b4b
Subsystem ID: 0x91a4
Revision ID: 0x0011
Link Width: x1
Link Speed: 5.0 GT/s

pci1103,622:

Type: RAID Controller
Driver Installed: Yes
MSI: No
Bus: PCI
Slot: Slot-3
Vendor ID: 0x1103
Device ID: 0x0622
Subsystem Vendor ID: 0x1103
Subsystem ID: 0x0001
Revision ID: 0x0001
Link Width: x1
Link Speed: 5.0 GT/s

Thanks for any insights.