Not sure if this is the correct forum section, but here we go...
I picked up a few of the Seeed XAIO SAMD controllers to see how well they would work. Windows didn't recognize them for driver purposes (unknown device, etc), and after a TON (read a couple days) of searching and weeding out dead ends and things that just didn't seem to work, I found that the driver located at Installing the SAM-BA USB CDC Driver for Atmel ARM Microcontroller in Windows 7 worked for me. You may have to right-click the driver link and use "save-as" to get it to save as an INF file. Just make sure you remember the folder in which it was saved. After following the driver installation procedure outlined on that page, my Seeed XAIO SAMD started working fine. I do on occasion have to hit the reset pins to get Windows to see it as a port again, but a small price to pay for the size and flexibility imho.
Hope this helps someone who was running into the same driver issues as me!
Edit: Its possible to see the Seeeduino Xaio show up as unknown device along with a new port called "AT91 USB to Serial Converter". This was the case with me from time to time when resetting or plugging in from having been unplugged. As long as the port shows up in your device manager under windows settings/system, you should be good to go.