Hello Atomic 207,
there is actually nothing to consider here. The unit still has one long PCIe slot (x16) and two short ones (x1).
A popular card at Digitec and also among our customers is the ASUS AC56.
ASUS PCE-AC56 (PCI-E x1)
The installation is very simple: remove the side panel when the PC is switched off, choose a free PCIe slot (slot below the graphics card), remove the slot bracket for this slot and insert the card. No wiring is necessary. Then connect the antennas and, after booting the PC, download and install the drivers. You can download them either via an Internet connection via LAN port (this is available on the mainboard), a USB stick on which the drivers have been downloaded from another device connected to the Internet or via driver CD, e.g. with an external DVD drive.
Alternatively, you can simply use a USB WLAN stick.