You’ll probably not be able to attach DAS to a minipc and be reliable, so all that’s left is a NAS. Or, obviously, you can get another pc that’ll take a number of storage devices other than m2 or that can handle a HBA of some sort. You want your mini pcs to stay cool as much as possible and putting in HBAs (in whatever way) or m2 devices (even worse) isn’t going to do anyone any favors.