In a nutshell, this robot is an experiment in building robots from RoboBricks2 modules
which is a project being spearheaded by a fellow in my local robotics club
as a way of making it easier for other club members to build robots. In this specific robot I'm using individual RoboBricks2 modules that provide motor control, motor encoders, LCD display, and serial communication (when tethered) to a PC. I also built three of my own RoboBricks2 compatible modules using AVR MCUs -- one to interface to the SparkFun 5DOF IMU and run a Kalman filter for sensor fusion, another for LED, Radio Control and button interface, and finally another for coordinating all the RoboBricks2 modules for overall robot control. The motors and encoders were purchased from Lynxmotion and the robot frame/case was constructed from aluminum tubing and metal project boxes.
I built the robot as you see it in the video over about four weeks and there were a number of issues I had to face. I'll look over the other threads you pointed to and see if it's better for me to put details related to building a balancing robot there. Unfortunately, I don't yet have the construction of the robot documented much, but I would be happy to share code and other design aspects of the robot if people have an interest.