So after more thread searching I find out that the 8940 supports only 1 NMVE drive. When I removed the on-board NVME, I was able to boot with the PCIe-NMVE adapter in either the x4 or x16 slot. Performance in the x16 slot (with Samsung 970 EVO Plus 1TB) was ~3.5 times faster than the x4 slot (970MB/s vs 3500MB/s). So all is good now but it would be nice to see two NMVE drives supported.
As many other posts have referred to, I am getting poor performance from my M2 nvme drive in either the m2 slot or in a 4x pcie adapter in 4x slot. Is there any possibility of plugging the 4x adapter into the x16 graphics slot and having it work? Harry
XPS 8940 4x PCIe-nmve adapter in graphic slot?