You can contact to Boundary Devices, if you
own a board, they'll send you the schematics.
Here is their contact page :
http://boundarydevices.com/contact/
There is also sabrelite board similar to
nitrogenx6 and here is its schematics :
http://boundarydevices.com/sabre_lite-revD.pdf
Here are the differences between Nitrogen6x
and SabreLite :
http://boundarydevices.com/differences-sabre-lite-nitrogen6x-and-som/
Hope this helps
Regards
Sinan Akman
That's correct, the Nitrogen board is manufactured by Boundary Devices.
You will be able to get the schematics from them.