Did anyone conclusively indicate that a USB 3 to NVMe adapter would work or not?  This adapter,  MyDigitalSSD M2X external USB 3.1 Gen 2 M.2 NVMe PCIe SSD enclosure adapter is listed as a 2 lane PCIe bridge chipset.  I understand that the Acorn uses 4 lanes so if this worked then it would be with degraded performance.

I would like to use a Acorn in standalone mode but I don't want to buy a new motherboard to support it and I don't have a free PCIe slot for the daughter card.

CreativeReef