Help with an Ambilight Project!

Beginner here.

Here's the project link:

And here's the LED WS2801 strip:

Ordered this strip, powering about 2 meters of it with a separate, switching 5V/20A supply. Will this work?

Also, I read on Adafruit that data moves in one direction and power can go either way, so should is it possible to skip grounding the Arduino to the main supply (I'm using a USB connection any way) and ground the strip and connect it to the supply through the other end(opposite the Arduino)?

I'm unable to ground the board using Molex connectors, they're all occupied. :confused:

Arduino Gnd and power supply Gnd must be connected, however you manage it. Make a Y-cable if you have to.
All Gnds on the Arduino are connected together - 2 on power header, one on header near the USB connector, and pin 6 on the ICSP header.