I'm late, but for future reference:
The 12big is too loud for my taste (louder than a Promise Pegasus2). I assume it's louder than a 6big, but can't say for sure.
Modification to make it more quiet:
The 12big has four fans of the type Noctua NF-B9 redux-1600 (3-Pin, no PWM). Noctua sells the NA-SRC10 Low Noise Adapter, a short cable that can be installed between the board and the fan that reduces the fan's speed (and therefore noise). I've modified my 12big with four such adapters, which helped considerably. The Seagate Ironwolf 4TB drives are still under 40°C while working hard to initialize the array, so totally within spec.
I've never noticed the fans ramping up or down, despite LaCie advertising them as being temperature-controlled.
I assume the same fan modification would work on the 6big, too.
LaCie's drivers currently work with Apple Silicon Macs, but it's unknown if the required kernel functions will be supported by macOS 14 and I don't assume that LaCie will want to write new drivers for the Marvell RAID controller contained in the 12big.
If you need a DAS, I'd recommend the Promise Pegasus line of devices.