The first version of the HMD had a few little problems :

• one screen flickers a little because of the connections
• PS3 eye camera capture quality is not so great
• elements on every face is a problem to put the device on a table
• some light is entering the device, from the borders of the screen.

So I decided to make some modifications :

• I added my DIY arduino hat (from my domotic project) because connections are good, there's a I2C level shifter that will be usefull, and both SPI channels are fully exposed. There are also an ATmega328 running at 3.3v/8MHz, and a Microchip MCP1702 is providing 3.3V to the board from the Raspberry Pi 5V. I think I will build a new board without the atmega, but with added features for the HMD (IMU, RGB and IR leds, on/off button, for instance).
• I replaced the PS3 camera with a Xbox360 camera (with IR filter and case removed)
• I created a cardboard "shell" to put on top of the screens. It's painted black on the inside, and I added a fixture for the camera module.

All these modifications allow me to put the raspberry on the top of the HMD. It's far less bulky, more robust and I can put it on a table...

With these modifications, I can say the issues I was facing are totally gone : image quality is far better, no more light is entering the device, and flickering has stopped.

Here are a few pictures, see more on this page.

Better look, isn't it ?