I had a bunch of Dell Rewards money that was about to expire. So I ordered a 2TB Samsung 980 Pro NVMe SSD to install in the SSD2 drive bay inside the X17, and I used the rewards money toward the purchase. I received the drive in the mail earlier today and installed it. That process was easy. But apparently the 980 Pro SSD does not get along at all with the Intel RST driver installed in the X17. For one thing Windows File Explorer will lock up when accessing certain folders copied to the drive. I wish I could have known about this before making the purchase. Samsung's Magician software listed the device conflict with Intel's driver, along with listing "N/A" for all the drive's diagnostic values. Looking around online I can see the conflict between the 980 Pro and Intel's RST drivers has been an issue for several months and doesn't look like it will be resolved. So I intend to return the SSD to Dell. I have no idea if my $150 or so in Dell Rewards will be restored.
Anyway, word of warning for anyone looking to stick a Samsung 980 Pro SSD into an X17 notebook. It probably won't work properly. The drive will install, show up in the BIOS and all of that. The performance just won't be very good or stable.
The only thing I've gained from this SSD adventure was getting a second heat sink for the second drive bay and it matches the OEM one in the SSD1 bay exactly.
Update: Dell gave me an RMA# and pre-paid FedEX label to return the SSD for a refund. I dropped it off at FedEx this morning. Not waiting around. Now I just have to figure out which specific models of Gen4 NVMe SSDs are truly 100% compatible with the Alienware X17 R1 and its drivers. I intended to have a pair of 2TB SSDs installed in the machine. I'm going to stick with the stock 1TB SSD in there for now.