Max capacity of G Raid Studio

[kyzygo]

Hi,

I have G Raid Studio Thunderbolt 2 with two 3TB drives (Kit PN 0G03501, Chassis PN 0G03496).

What is the maximum capacity drives it can take? Can I upgrade it to 2x8 TB drives? 2x12 TB drives?
Any suggestions about the type of HDD I should buy?

Thanks!