Moving external disks to a DAS?

[TheDreadPirate]

For THAT many drives, you definitely need a workstation or server CPU just for the PCIe lanes for all the HBA cards you'll need to connect them.

Honestly, I'd choose a 1000 series Ryzen Threadripper or something and case like a Fractal Meshify 2.  1000 series Threadrippers are cheap, 64 PCIe lanes, throw in as many HBA cards as the E-ATX motherboard can fit, the Meshify 2 can mount....12(?) hard drives internally.

My much more tame setup in a Meshify 2.