Newbie, Rest pose problem

I’m a Motionbuilder pro, and for a freelance project i need to transfer mocap data to some Avastar rig in Blender in order to export BVH file for Second Life.
However, my blender knowledge is very limited.

At one point, the tutorial asks me set both the rig and the imported BVH to T-pose by setting them both to rest position, however the rest position for the BVH file for some reason is rotated on X axis by 90 degrees.

I’ve spent countless hours today searching for a way to reset the rest pose to no avail.

In Motionbuilder, the rest pose is called Stance, and it’s properly set.

…additionally, applying the T-Pose as rest pose completely destroys the animation.