I've set up a G-Speed eS Pro XL12 (which has an internal SAS expander). This is similar to having three G-Speed eS Pro enclosures with a SAS expander. So while I haven't tried your specific setup, I am confident that it will work with a compatible expander.
If you haven't purchased the G-Speed eS Pro units yet, would you consider getting an XL12 or XL16 version instead? While it may not be less expensive, it is more robust with redundant PSUs.
Best,
Alexei,
DV411