I see that the MD600 can be configured without mirroring to yield 4TB of storage. I wonder if it will support 3TB drives and also what are the expansion ports for, They look like USB ports, but no mention of them in the datasheet.
3TB depends on whether the current Sooloos range can support larger drives.
My old Infrant NV+ has a similar problem. It's limited to 2TB (I think actually 2.2TB, but no one makes those). Larger drives require
GPT support rather than
MBR support, and there is little point in rewriting the code for GPT give the age of the architecture of the NV+'s hardware.