Ok.
I think we narrowed the error to the gyros scale.
Try to get YPR integrating gyro's measures. Then you will see if it is deg/sec or what constant you have to multiply them for.
Try this setting the scale to 250 degrees, 500, and 2000.
Im interested only in the gyro's estimate, do not fuse it yet.
To check scale you can do a simple experiment: try to rotate your board at constant speed. For example rotate it 360º in 10 sec (try to do it at constant speed), and you know you should get something close to 36º/sec