You are correct that the 750 is PCIe, but it requires a connector that connects to the M.2 slot on the MB to run at full potential.
M.2 is PCI-E but PCI-E is not M.2... Well, to put it simply, these types of SSDs need four lanes of PCI bandwidth, regardless of how the drive ultimately connects to the CPU.
The first variant, called the AIB or add-in-board looks kinda like a GPU and slots in basically the same way, into one of the PCI-E slots that provides 4x lanes of bandwidth, and that's all that's needed.
The second variant connects via SF8639 connector aka "U.2" as of April this year, but there are currently no motherboards with this connector outside of the server space, however conversion cables are available to M.2 type.
M.2 is a format initially developed for SSDs for compact devices, but in a full-size PC it's not recommended to use them due to heat issues, the Samsung XP units in particular can easily reach over 90°c.
Overkill with room to grow, but the next size up is really pricey, and the next size down is only a little more affordable.
