Use Crystal disk info to find out what is installed and then you will know what you need when replacing the 256 GB . Crystal disk will tell you which interface is used.
http://crystalmark.info/software/CrystalDiskInfo/index-e.html
The Samsung PCIE unit that you mentioned is not viable as a direct replacement in the HP Turbo Z adapter card.
It uses an NVMe interface instead of the MLC nand that the Turbo Z M.2 SSD uses.
Here is an article that will give you sone insight on what I am talking about.
http://www.computerweekly.com/feature/MLC-vs-SLC-Which-flash-SSD-is-right-for-you