f32 IGUISpinBox->getValue()
This is what I used instead of IGUITable because of that getValue method.  It returns an Irrlicht f32 which is a 32bit float that converts nicely to Bullet's btScalar float.  It's a bit clumsy but it works, with minimal complexity. 

     Now my focus is on the playerCube control.  This is the heart of the gameplay, and what will define kyuplex.  I'm afraid applyCentralImpulse isn't cutting it anymore, because I need to implement a constraint system, that will keep the cube level below a threshold. 
     I'm trying btGeneric6DofSpringConstraint first.  Struggling with how to combine the rigidBody dynamics and constraints with player input and control.