I didn't like how the gamegrrl was made without a speaker. I added a small amp like this one. http://www.suntekstore.com/goods.php?id=10019845&utm_source=gbus&utm_medium=paid
I powered the amp from the same 5.2V output from the voltage booster, I connected the input to the headphone jack on the pi and wired the speaker to r- and r+. You can hook the speaker up to L- and L+ if you want. Just don't hook up both speakers to both outputs. I added a 10K resistor between the speaker and the amp output to keep the speaker from blowing. The volume is good. If I ever find a small potentiometer I will add a volume control to this build. For now, it is the perfect volume level. The speaker is the .5W metal speaker you can buy at adafruit. Check it out here: https://www.adafruit.com/products/1890
Its an easy build. Just use extra wire so that you can route them around the button pads while closing the case.
Instructions are in the description.