a brief examination of Myo's source files shows that quaternion components are stored as x, y, z, w. This is the same for Cinder's implementation, provided by the GLM library. So you should be able to simply cast a Myo quaternion to a GLM quaternion, provided you use the same precision (float or double).
glm::quat q = reinterpret_cast<glm::quat>( myoQuaternion );
To use the quaternion, simply convert it to a 4x4 matrix. GLM has the
toMat4() function for that:
gl::rotate( glm::toMat4( q ) );
// draw stuff