*** Update #16 ***
Today, I was able to complete soldering the USB DAC, Teensy and audio using original pot and 3.5 jack.
I was looking for the best spot to put the Teensy that will minimize the amount of visible wires. I thought where could it be but parallel to the controller PCBs traces! Instead of soldering the wires straight through the trace holes, I decided to solder the wires on the surface, with the soldered wires forming a "U". This way, I can still lift the Teensy as I test it, making the soldered wires acting as a hinge.

[spoiler="Completed wiring the Teensy, USB DAC, and audio"]

[/spoiler][spoiler="Testing for boot..."]

[/spoiler]
Also did some test fitting...[spoiler="Test fitting - side view"]

[/spoiler][spoiler="Test fitting - top view"]

[/spoiler][spoiler="Test fitting - showing location of Teensy and JST connector"]

[/spoiler]
One of the reasons why I placed the PowerBoost at the top behind the screen is to minimize additional work for seeing the PowerBoost indicators LEDs. Instead of boring another hole for the PowerBoost blue LED power indicator, I thought of using a clear power button and hope that the blue LED will shine through. Turns out it's bright! Picture below shows the Kitsch-Bent clear power button against the PowerBoost blue LED. [spoiler="Effect of Kitch-Bent clear power button against the PowerBoost 1000C power LED"]

[/spoiler]
Just a few more work to do wiring the LCD remote and battery connector.
