Yes, you can put x2 of M.2 SSD (with heatsink) and up to x4 of 2.5" SSD.  Additional dual drive brackets and cables are required. [IMAGE]
how many storage drive can you put in my XPS 8950? can you put 2 M2 Storage  and how many SSD drives? and can you use the new Samsung 990 M2 with heatsink in both M2 pcIe connectors?
XPS 8950, storage drives